The Illusion dispelling rune doesn't dispel Invisibility Sphere

[SteveMaurer]

It does dispel normal invisibility though.
I'm pretty sure this is just an oversight.

[Dorganath]

It seems it's because Invisibility Sphere is its own sort of effect as far as the scripting engine, and isn't typical "Invisibility" from the caster's perspective.

Anyway, attempting a fix for the next update.