I wanted to make a cloak spell that would dispel invisibility, so I made first a separate cloak (which I made into an ability), and then a concentration, aimed spell that would dispel all spells with the keyword "MagicInvisibility". I gave this to an NPC, and tested it in game.

It worked fantastically well - other NPCs that I gave the invisibility effect to lost that effect, and those that I re-gave invisibility to (through a separate invisibility other spell) also lost that effect.

My character, however, was unaffected.

I remained invisible for the duration of the test. Though I tried adding new conditions to the magic effect (i.e. GetID Player == 1), I still couldn't get the player to lose their invisibility magic effect.

Why was it that my character was so unaffected, when all the other NPCs were? I cannot understand this for the life of me.

So, who hit your player with the "dispel" effect?

If you used an "area" effect: Those do not work on the person who cast them (unless the spell also has a "stagger" effect).

I gave an NPC the cloak spell which should have dispelled invisibility of all actors nearby (much as a flame cloak deals fire damage to those nearby). My character didn't cast the cloak spell - that would just be completely silly.

It stands to reason that if my character were to stand near the NPC with the active cloak effect, that my character would have lost its invisibility effect. Yet, it didn't. Why?

Cloaks work this way: Cloak (spell) -> Cloak (MGEF) -> Some spell (spell) -> Some spell's MGEFs (MGEF)

What are all the conditions on your cloak (spell), cloak (mgef), some spell (spell), some spell's mgefs (mgef)?

I purposely gave them all no conditions - I didn't want anything to possibly complicate matters. To keep it as simple as possible, I made the cloak an ability and assigned it to a race of NPCs, just to ensure it would always be on.

I am guessing this is one of the Magic effect archetype quirks: Some have inbuild conditions (such as: only affect hostile targets).
You could try giving the NPC-Race the standard-issue flame cloak (there should already be an ability for that: The atronarch flame cloak) and see if that spell damages you. If it does not, that probably means cloak spells only affect the player if the player is hostile to whoever has the cloak.

On second thought: That is very likely the case, as your own summoned atronarchs obviously do not damage you. The other possibility is that whether or not the cloak affects the player is governed by the second spell's (the one cast BY the cloak) MGEF. I am guessing you are using a script archetype effect. Change it to a stagger effect, see what happens.

I haven't tried the stagger effect yet, but I will post as soon as I do.

I did give several NPCs the Flame Atronach's abilities (including the fire cloak), which didn't affect me in the least. It's odd, because the secondary spell for that fire cloak has a condition for the target: ishostileto [target] == 1. So... even then it should affect me... Especially since it's a value modifier, not a script.

'S IsHostileTo [ TARGET ] == 1'

'Subject' (the one hit by the effect) is hostile to 'Target' (the one who cast the effect). I don't think the game is able to see whether or not the player is hostile to someone, just like it can't tell when the player is in combat or who the player's combat target is.

If you check the regular cloak spells (not the ones used by the atronachs), they work on the player.

But mine don't have that check. :S I only added it once during testing, and it's removed now.

Not to mention, it's in the MGEF for both the Atronarch's secondary spell and the regular player-used Flame Cloak's secondary spell.

Sorry, I still don't have any idea about why your spell wouldn't affect the player. But I'm sure that at least the regular frost cloak spell works on the player.

I can confirm this: Made an ability "copy" of the Flame cloak spell, removed the "ishostile" condition, now affects everyone, including the player (the mass carnage in cities this causes is fun to watch ^^).
Tested with both value modifier and script archetype effect.
The question then is: what's the difference between the ability I just created and yours?