A lot of games will usually have a "known buglist" thread somewhere - this does a few things, including letting players know that the bug has been acknowledged by the company (and so the chances of a fix are more hopeful), and saves people creating new threads on issues already known. Here's all the issues I've spotted so far, if you have an issue not on the list and want it adding here, please reply to this thread giving as much detail as you can. My hope is this may encourage Bethesda to maintain their own official "known bugs" thread. I'm not by any means claiming this is a "complete list" - but at the moment this seems to be the most comprehensive list in one location on the forums?

Graphics, Textures, Animations etc.
* There is a huge and disproportionate FPS hit upon entering towns for many users (may be related to/affected by items below).
* Light-sources (eg candles, fireplaces) seem to cause a disproportionate slowdown/FPS hit even on extremely high-end systems, just for 1 or 2 lightsources.
* Shadows are extremely low-resolution and pixellated to a ridiculous degree (many people seem to think shadow-rendering is done by the CPU instead of the GPU, which could explain the above, other claims this is not the case - there is some strange CPU bottlenecking on powerful machines though?).
* A combination of more than a few NPC's close together, and light-sources, causes crazy FPS hits (this is really the combined effect of the above three items?).
* Mouse Y-Axis sensitivity appears locked to FPS/performance - this can cause the mouse to require you to use the entire height of your mouse-mat just to look up by a couple of inches at times.
* Quad core CPU's don't appear to be being utilised (despite the recommended system specs requesting a quad-core CPU?).
* .Exe is not flagged as large-memory-address aware (so despite recommended system specs suggesting high RAM, the client will never use that much RAM - users can patch this themselves with 3rd party software in seconds, why can't it be official?).
* Some GPU's seem to be being incredibly under-used, despite apparent lag/FPS drops/slowdown issues - is this related to graphics-tasks being offloaded to the CPU because this is beneficial on consoles?
* Sometimes when walking around, ground textures do not load in quickly enough, and you can be stood on a crazily blurred out, almost single-colour texture for a while (anything up to a minute), before the higher-resolution ground textures load in over them.
* Many heavily used textures seem to be extremely low-resolution (this may not be a bug, it may be that no high-res textures ever existed).
* Anti-aliasing at certain settings causes a strange blue-line glow/outline around your character and any items you are holding.
* Character animations for sprinting while dual-wielding spells or weapons looks ridiculous and broken.
* Bloom levels in the snow can go too high - causing snow to almost blind the player even when there's not much snow (intentional? Emulating real-life "snowblind"? ).
* The system that auto adjusts brightness (dims/brightens lights as you look and move around) - any chance of a way to disable this? It seems hyperactive on some systems.
* The small arrows for tracked quests that appear on-screen over doors/NPC's etc. sometimes fail to show at all - unchecking and rechecking all tracked items in the journal sometimes fixes this.
* Sheathing animations for dual-wielded weapons, in third person, appear broken/missing.
* Number of (seemingly random) issues with LOD - flickering can be observed at certain distances, but not others (generally with the mid-range LOD stuff?).
* Certain sets of armour on certain genders/races have clipping issues, as do certain helmets with certain hairstyles, badly jarring when playing in third person (try a heavy male character in Orcish armour for example).
* Water doesn't always load in - sometimes lakes can look like they have been completely drained, and you can walk to the bottom of them and still see clear-as-day from one side to the other.
* Possibly cause by a conflict with a certain batch of ATI graphics drivers, but there is a "black screen of doom" bug that crops up after various minutes/hours of play for many users (see http://www.gamesas.com/index.php?/topic/1263776-computer-black-screening/)

Core Engine/Physics Engine
* Many random crashes-to-desktop - these cause no error messages, it just throws you instantly back to desktop with no notice. There may be many causes of these, some listed elsewhere here, but the outcome is the same.
* Mammoths occasionally shoot 100 feet into the air, and then drop down dead - possibly when two mammoths are following too closely, the one at the back is launching the one in-front of it into the air when they try turning?
* Dragon bones can be seen dropping from a huge height and landing again when you re-approach an area they were left in (and sometimes they'll appear at fast-travel locations when you zone-load in, NOT where they were killed).
* Sometimes simple acts such as opening a door will launch all objects off of nearby shelves/tables etc. that were within a certain distance of the door - seems to be related to how fast your FPS is?
* Objects can get stuck in other objects and will constantly be trying to "jump out of the object" (sounds like two objects banging together over and over without stopping).
* Running over objects/random clutter on the floor can launch them like a cannon has fired them - you can actually injure and even kill your own character with this at times.
* A strange bug can cause objects to get "stuck" to both the player character and NPC's (eg an NPC chopping logs might start getting log-graphics stuck all over it's hands, a player can get animals stuck to parts of their body).
* The instant anything is off-screen, it seems to forget where it was - try very quickly moving your camera back and forth between two people either side of you, you'll see they keep "jumping" into different positions.
* Sometimes the above feature (where things happen differently when off-camera) actually happen on camera - you can be talking to an NPC and suddenly another NPC will warp in in-front of you, an NPC that was elsewhere in the village/building.
* Giants can launch the player hundreds of feet into the air like a rocketship in a single-hit (20 feet in the air would be fine, but they can hit you higher than the throat of the world mountain).
* V-Sync (or iPresentInterval) seems to have a huge impact on many other things ingame, such as the time-of-day the "next day" happens at, mouse sensitivity, etc. - why/how?
* Sound levels are far too low on certain systems, without any way to increase the volume beyond an extremely low level.
* Horses have ridiculous physics - you can climb up near vertical cliffs on a horse at crazy angles, though horses can sometimes die just from falling off a three foot high stone.
* If you kill a character with any form of knockback effect, you can sometimes "push" their corpse through the gameworld, and cause their corpse to be unretrievable or lootable. Is this down to some "speed" setting of item movement - eg a speed of "10" moves it 10 "measurements" per cycle, without any checks on if they would have encountered a floor after say, 7 "measurements" - so they skip right through the world?
* Casting spells such as "Raise Zombie" on a dragon's skeleton causes it to shoot into the sky.

Interface, UI & Controls
* Selling/buying is bugged - if you hover over an item the NPC is selling, and then scroll down the far-left list onto your own items but DON'T move the mouse to the right (so DON'T hover over an item you actually have) - and then tap E - you gain gold for the item the NPC owns, and you can spam it - as if you are selling the NPC's own item back to them. The same bug may also allow item duplication/crashes using the same technique on containers.
* The bizarre fact that the global map can be scrolled with WASD but not mouse-dragging, while the local map must be scrolled with mouse-dragging but not with WASD.
* The inability to navigate the perk trees with any reliable and logical sense with a mouse & keyboard, and many other UI inconsistencies and issues with M&K and large screens.
* Appears to be no way to sort the inventory - can't sort by items worn, item weights, item values - stuck with pure alphabetical text lists. Not even small icons representing "Item types" next to the items?
* Mouse-clicking in menus is very buggy - sometimes mouse-clicking directly on items in the UI fails altogether. Other times is works for some but not all. Yet more times clicking anywhere but exactly on the text itself causes the menu to load. Using the keyboard seems to be fairly reliable - it seems to be the mouse controls that are very broken in the UI.
* If you use WASD to navigate the UI and hit enter, but your mouse is over something else in the UI (an item, a dialog option, etc.), hitting enter can select the item the mouse was over rather than the one you used keys to navigate to (and the reverse is sometimes true).
* Key remapping doesn't seem complete - many interface related key presses (eg favourites and hotkeys) screw up if you remap those same keys (eg remapping the F key that changes to third person, interferes with the F being used to favourite things, changing the WASD keys to cursor movement doesn't allow you to use cursor keys for lockpicking, etc. etc.).
* Should be far more hotkeys open to PC users for the favourites/quick-list (how about supporting ctrl+key, shift+key, alt+key to expand the list massively?).
* Players should be able to hotkey a combination - eg hotkey a shield&sword combo, or hotkey a dual-wield combo.
* There is no way to quickly check buffs/debuffs - without a painful chore going through the magic menu.
* The "R" key to unlock dragon shouts, even though you have souls, occasionally doesn't work (may just be from key remapping, but even without remapping the R key, this can still happen, spamming the R key sometimes unlocks a shout).
* Key-bindings seem to "break" for hotkeys if you try to switch from "magic in one hand weapon in the other" (and possibly other dual-wield combos seem problematic with the favourites hotkey system?)
* If you middle-mouse-wheel while using the enchanting station, it can zoom your character out and cause your character to be permanently stuck even after trying to leave the station.
* Appears to be no simple way of seeing if you already know a spell listed in a container/NPC etc. - surely spell tomes for spells you already know could be greyed out (or if items had small thumbnail icons by their names, as they should, the icons could be greyed out).

NPC's, Companions, Creatures and their AI
* Sometimes some NPC's (not followers) get 'stuck' following you around (particularly with Farkas) - they will persistently try to talk to you over and over, which interrupts you attempting to fight/talk to others/do anything at all.
* If an NPC is in the middle of a random dialog line (the ones they say as you walk past) when you zone into a new location (particularly a player house), the NPC will actually zone into the house with you to finish what they were saying, then try to leave again.
* NPC's frequently do their animations half-way in objects, or many feet away from the objects they are apparently interacting with - eg appear half-way embedded in the floor, or leaning on a post 5 foot away, or animations bugging causing them to spin round-and-around while apparently sleeping on a bed.
* You can place a bot/basket/tub etc. over everybody's head (by dragging it over them), they won't object to this at all - but will no longer be able to see, so you can murder their family or rob them blind of all their possessions without them making a single complaint, they'll just stand their happily with a basket over their head.
* A single giant and mammoth can takedown a dragon with relative ease (should dragons not be the toughest encounters?). Also seen a single ice-troll solo a dragon.
* Marriage sometimes fails to work on characters that should be "marryable" - also there is a distinct lack of certain possible partners of certain races-genders, your partner will sometimes disappear altogether after the wedding and never reappear, and the entire marriage systems seems to be about as deep as a single variable.
* Headless horseman ghost sometimes freaks out and flies through the air at crazy speeds - possibly related to the general broken physics of horses?
* "Fugitive" random encounter can approach and open dialog with the player by surprise, while the player is in the middle of combat with others, often resulting in death. (needs an "is in combat" check before the fugitive tries talking to you).
* Horses, particularly stolen ones, have serious problems upon dismounting - dismount a stolen horse and it can shoot hundreds of feet away instantly.
* If you ask a companion to leave, it occasionally doesn't flag your character as having "no companion" - and trying to get a new companion (or even the same one that left you) fails, as you are told you already have a companion.
* Companions can sometimes get stuck in certain positions, eg the death/lying down position - but continue to follow you around. So you can have what looks like a snake-person sliding around following you everywhere.
* Companions don't always enter through the same door - eg you can enter a large fort that has two entrances, and your companion will zone in through the back door and aggro half the fort for you.
* Companions (and other NPC's following you) can stand in the doorway of a small room you entered and block you in the room - sometimes you can get the NPC to move if you run around the edges of the room, but not always. You should be able to push your own companions/followers out of the way by running into them.
* Companions sometimes get stuck at certain stages in dungeons, and instead of continuing to follow you, will run back to the start/get stuck in a certain part, as if there are pathing issues (and you'll have to finish the dungeon alone).

Perks, Skills, Your Character & Your Items
* The heavy armour "weightless armour" perk constantly forgets itself, which causes your character to become overburdened until you flick your inventory on & off again.
* Smithing an iron dagger or hide bracers nets as much smithing exp as a set of Daedric armour - you can just spam single ingot & strap daggers all the way to 100.
* Arrows, ice shards etc. get stuck in your character seemingly forever, despite zone-loads, sleeping etc. - you can have giant ice-shards or arrows sticking out of your head forever.
* Other graphical effects can also get stuck on your character - eg if you get hit with frost or fire spells/effects, sometimes the graphical effect gets permanently stuck to your character even after the DOT/effect has worn off.
* Using a bow & arrow in third person crouched fires arrow from a point behind and below your character, so it can get stuck in objects or the floor depending what angle you fire at, rather than firing from where your bow actually is.
* Wearing a hood and a mask at the same time causes your character's head to turn invisible.
* Certain hood/mask combos allow you to wear the equivalent of 2 helmets/2 masks at once (some sort of slotting/slot number issue relating to helmets being considered different to masks on some items but not all?).
* The "Aura whisper" shout seems to give your character unnatural, brightly glowing eyes, with no way to remove them.
* Some save-games are randomly disappearing - restoring backups can fix this, appears to be some problem in the save-function that crash that function and cause corrupt/no saves?
* The knock-down effect of shield-charge sometimes stops working, seemingly at random.
* At times, the player can no longer get rested/well-rested buffs (despite having no diseases, and not being a werewolf or vampire) - is this impacted by changing stone-signs?
* Custom named weapons default to their base name if you get disarmed with them... likewise if you custom name three similar items (same base/same enchants) with completely different unique names, and drop them all - their names get "merged" - the game seems incapable of keeping track of unique item names the moment the item is no longer on your character.
* Total charges/prices of enchanted items are sometimes loss when changing cells/loading new cells (possibly related to the above when you have more than one item of a similar base type but different enchant/charge quantities?).
* Dropping a soul gem you filled onto the floor can empty the soul gem.
* Even after curing yourself of being a werewolf, NPCs will still make comments about you having "hair growing from your ears" - a certain werewolf related flag is not being cleared?
* Other illnesses have the same "stuck on" problem as above - eg NPC's may comment on you looking sickly even after curing a disease.
* The "Matching Set" bonus for Ebony armour-sets is broken.
* Your reticle sometimes displays incorrectly if you, for example, are sneaking, and quickload a save where you are not sneaking - the "character state" is merging/confusing the reticle system.
* Stormcall shout - is it meant to have such a huge area, and hit everything including neutral NPC's, friendly NPC's, companions and even your own horse? It makes the call unusable in many/most situations.
* If you are over-encumbered, you cannot move at all if you are in 3rd person view (but can move slowly in 1st person view).
* You can have infinite magika by removing and then re-equipping an item that has fortify magika - drain all your mana, then use your favourites/quick bar to remove and re-equip the item that had fortify magika, you'll instantly get however much magika that item fortifies you by given to you. (probably works with health and other similar items if you remove and then re-equip them).
* "Blessing of Talos" states that time between shouts is reduce by 0% (zero percent).
* Changing to "beast form" sometimes gets confused - you visually change, but get no benefits of beast form, and you are automatically equipped with (random?) weapons/spells you have - but are unable to use them properly due to being in beastform.

Environment/Furniture/Interactable Items
* The bookshelf is difficult to fill the bottom/middle shelf with books if you fill the top shelf first (and sometimes leaving the house and coming back later causes the bookshelf to appear empty visually, while still containing the books).
* Buying all furniture for your Whiterun home breaks the ownership of the "guest bed" - eg Lydia will no longer sleep anywhere.
* Items don't always stay where you last moved them in cells (particularly important for your own house) - they tend to stick to where they were when you first dropped them/they first appeared in the cell - they will revert to this position if you leave then re-enter the cell (rather than remembering the position you last moved them to).
* Some torches on walls, that look identical to any other torch-on-a-wall, are not interactable (cannot be taken or turned off) - eg some/all torches in Pinewatch.
* The small wooden handcarts dotted around, that often have items in the back of them (there is one in the tutorial/intro cave just before the bear), seem to be as light as feathers despite being quite large wooden items - nudging them just slightly can send them flinging off into the distance as if you had just shot them with an RPG.
* Walking around certain parts of Morthal can cause your character to warp and become stuck above the hall of the vigilant, with no way to continue except to reload a previous save.

Terrain/Areas/Locations
* Certain areas seem to have their own CTD issues relating to objects/creatures being spawned half-way into walls and floors or something.
* Bonechill passage will cause a CTD almost guaranteed after moving beyond the first chamber and heading to the 2nd/final chamber - however playing in windowed mode appears to fix this?
* Wolfskull Caves appears to have a large area of missing texture/missing objects (can see through into a "graphical void")
* Ironback Hideout has no bedrolls/anything under the tents (it clearly should have - there are no beds anywhere for the NPCs to use, every other similar location has).

Quests
* There are many items flagged as quest-items that remain flagged even after completing the Quest, and some weigh lots (eg 20lb for a main questline item), and can never be removed dropped or sold, causing a permanent loss to your total carry capacity.
* Quest-items sometimes become invisible in any and all item lists (containers, your own character etc.) - they simply will not show in any lists, which can break many quests where you have to loot a specific quest item etc.
* Sometimes the main-questline when your character first talks to the monks and is meant to extend unrelenting force abilities, the monks actually do not transfer any ability to you at all and the questline is stuck from that point - a reload and trying again can sometimes randomly fix this (seems linked to the function that lets you absorb shouts and souls from dragons/dragon walls - this sometimes doesn't trigger elsewhere in the game, but particularly on this quest from the monks).
* "A Cornered Rat" - When the NPC "lets you in to talk" - he sometimes doesn't actually let the player in, just closes his hatch and nothing else happens - the quest is permanently stuck then.
* "Loud and Clear" - you can finish this quest but not be given and have no opportunity to receive any followup quests at all.
* "Blood On The Ice" - the graveyard scene sometimes fails to load, causing the quest to get stuck.
* "Gauldur Amulet" - starting this questline/being at a certain stage on this questline can cause a CTD every time you attempt to enter Whiterun, making Whiterun inaccessible.
* "Forsworn Conspiracy" - quest can break if you pickpocket the note during the escape - the quest then updates telling you to check the body, but as you already have the note, you cannot trigger the quest to continue.
* "Markarth Conspiracy"/"The Forsworn Conspiracy" - the guards that arrest you never leave the shrine - you can be arrested, sent to the mines, complete that stage of the quest - but re-enter the shrine and the guards are still there and the whole process repeats, over and over.
* Winterhold College Quest sometimes breaks when you should be starting "Containment" - the necessary triggers simply fail to activate.
* "Blessings of Nature" - the old tree will remain in place with the new sapling growing inside.
* "Battle for Fort Hraggstad" doesn't always allow you to continue to "Battle for Solitude" - it just ends the questline with no way to continue the quests.
* "Season Unending" making a truce can get stuck - Ulfric won't talk to you - possibly he is getting stuck stuck with the joining the stormcloaks quest instead (even if you don't intent to ever join the stormcloaks).
* "Brelyna's Practice" - when Brelyna asks to practise on you, the quest can get stuck at the point where you are supposed to wait for the effect to wear off (no effect listed in active effects, no amount of waiting/zone loading moves the quest forward).
* "Under Saarthal" - casting a fire based spell at the wall can cause a game freeze for some users (frost based spell apparently works fine). Other people have reported that no amount of spellcasting affects the wall at all, other that dual-casting is the only way to fix it.
* The Bard's Quest can become stuck if you have already picked any of the needed instruments up before receiving the quest (game does not acknowledge that you already have the items).
* Completing quest-lines for Companions, Thieves Guild, other major areas etc. appears to have no benefits - re-entering the Thieves Guild, Companion Halls etc. you still get passing comments as if you have just been dragged up from the gutters and are a nobody - is this because of further quests not appearing, variables not being flagged, or is there simply no dialog lines/scripted events to occur once you have achieved "great deeds" for these guilds?
* The "fortify" buffs you get on a particular mage guild quest can sometimes get stuck on your character, giving you the equivalent of permanent, infinite magika.
... many, many other broken quests or specific questlines not yet listed.

I would like to ask you to specify the LOD flicker part:
The issue is not random, it happens for specific (if not all or most) mountains at a certain distance (the "mid-range LOD distance" is correct). It's most noticible with the mountains west of Whiterun.
It happens for mountain snow LOD, nothing else.

Thanks, I've clarified this one hopefully more accurately now. Where it's a bug I've not actually encountered myself (though I've encountered a scarily large number of these myself ), I'm doing my best to look up threads and other posts that relate to the bug to try and narrow down any details/causes before adding it to the list, where possible.

* Key-bindings seem to "break" for hotkeys if you try to switch from "magic in one hand weapon in the other" (and possibly other dual-wield combos seem problematic with the favourites hotkey system?)

Don't forget teh invisible effects fixed by the unoffical patch released in this thread

http://www.gamesas.com/index.php?/topic/1257882-patch-1-unofficial-bugfix/

I found that game works incorrectly for some hardware and drivers, so did a patch. For example it fixing invisible fire from dragons, magic fx, volumetric fog and other effects, black dots and "fence" on the screen on ATI and NVidia cards, long time freezes per 3-5 minutes of gameplay, some sound problems. In future i'm planning to add new visual fx to this game.

I believe he is sticking to bugs found in the unmodified game. It is waaaay too hard to keep track of every single mods problems.

Interface, UI & Controls
* The bizarre fact that the global map can be scrolled with WASD but not mouse-dragging, while the local map must be scrolled with mouse-dragging but not with WASD.

Interface, UI & Controls
* The inability to navigate the perk trees with any reliable and logical sense with a mouse & keyboard, and many other UI inconsistencies and issues with M&K and large screens.

Interface, UI & Controls
Appears to be no way to sort the inventory - can't sort by items worn, item weights, item values - stuck with pure alphabetical text lists. Not even small icons representing "Item types" next to the items?

Interface, UI & Controls
* Mouse-clicking in menus is very buggy - sometimes mouse-clicking directly on items in the UI fails altogether. Other times is works for some but not all. Yet more times clicking anywhere but exactly on the text itself causes the menu to load. Using the keyboard seems to be fairly reliable - it seems to be the mouse controls that are very broken in the UI.

* If you use WASD to navigate the UI and hit enter, but your mouse is over something else in the UI (an item, a dialog option, etc.), hitting enter can select the item the mouse was over rather than the one you used keys to navigate to (and the reverse is sometimes true).
* Key remapping doesn't seem complete - many interface related key presses (eg favourites and hotkeys) screw up if you remap those same keys (eg remapping the F key that changes to third person, interferes with the F being used to favourite things, changing the WASD keys to cursor movement doesn't allow you to use cursor keys for lockpicking, etc. etc.).

Interface, UI & Controls
* Should be far more hotkeys open to PC users for the favourites/quick-list (how about supporting ctrl+key, shift+key, alt+key to expand the list massively?).

Interface, UI & Controls
* Players should be able to hotkey a combination - eg hotkey a shield&sword combo, or hotkey a dual-wield combo.

Interface, UI & Controls
* There is no way to quickly check buffs/debuffs - without a painful chore going through the magic menu.

Interface, UI & Controls
* Key-bindings seem to "break" for hotkeys if you try to switch from "magic in one hand weapon in the other" (and possibly other dual-wield combos seem problematic with the favourites hotkey system?)

Interface, UI & Controls
* Appears to be no simple way of seeing if you already know a spell listed in a container/NPC etc. - surely spell tomes for spells you already know could be greyed out (or if items had small thumbnail icons by their names, as they should, the icons could be greyed out).