Let me start off by saying that I don't play Skyrim the way most people do (with this character). He is a stage 4 vampire. He been vamped out since level 1, right now he's 59. I charm my way through towns to sell things, and Invisibility is my best friend more often than not. I've seen my fare share of odd things happen to me in the game. And while some may be legitimate bugs, some I attribute to my unique play style (just a theory of course). I once walked into a town, and a kid saw me and screamed "Leave me Alone!", then the entire town attacked HIM! Which was very amusing to me (it's just a game after all). The best part was when people watching the town attack this kid starting shouting "My money's on the big one!". Very funny. But anyway, I was wandering around Dragon tooth crater I believe, and I stopped to get me a Dragon Soul. As I charged the dragon, I realized he didn't fight back. I continued drain his health until there was nothing left. But I could not kill him. No matter how many times I hit him, nothing happend. He had no health. I summoned Frost, Flame, and Storm Atronach's, along with a Dremora Lord. They all paced around the dragon with a combat stance, but that was it. They wouldn't attack him. I looked on my map and found a nearby Storm Cloak camp. I wanted to lure a small army to the dragon (which isn't hard to do being a stage 4 vamp). About half way to the camp, I heard the wooshing sound you get when a Dragon flies over head. I looked up and sure enough, it was the same Dragon with no health. He didn't roar, and ultimately would not land. He followed me to the camp and Storm Cloaks started shooting arrows at him. And nothing happend, he just kept flying around me. (I was invisible to avoid the Storm Cloaks turning on me) I reloaded and attacked the same Dragon, with the same results. Has anyone else had problems with Dragons not attacking?

No but, cool play style I might check it out.

They probably look at that paragraph and leave like I'm doing.

Was he a quest-related dragon, perhaps?

I like the idea of using charm and invisibility as a vampire... might have to try that next playthrough....

I've had dragons land to kill a troll or a giant, right next to me, and not attack me. This has happened a couple of times. The look at me, then fly off. In both instances, it happened after the MQ is done, but I've no idea if it's related to Paarthurnax recruiting a few to his side, a glitch, part of the game, or results from the Deadly Dragons mod.

But I've never seen one that wouldn't die.

Not all dragons are set to be hostile. They fly around, make some noise and then fly off. While in this condition, I don't think they have the same fight AI that a dragon that is set to be hostile does. It may be the game makes them unassailable which makes sense as even arrows and Dragonrend will not get these dragons to land or fight. It would also explain all the behavour you desribed in this encounter.

The reason reloading does not work is the save, probably an autosave, was made after you entered the cell that that the non hostile dragon was in so it will always be there and behave that way.

In other words, make a new save slot and you will always have a dragon to play with. Like say you want to try a new attack strategy or something.

I think the glitch here is that you were able to approach the dragon and hit it, not that it behaved the way that it did.

The dragon he's talking about is at Dragontooth Crater. It's guarding a Word Wall and should be hostile as soon it detects you... it's not some random dragon who's going about his business and doesn't want to be bothered.

However it appears there is a known glitch with this particular critter:

http://www.uesp.net/wiki/Skyrim:Dragontooth_Crater
http://www.uesp.net/wiki/Skyrim_talk:Dragontooth_Crater


There is a bit more info at the links above, but doing a search for dragontooth crater might yield additional tips.