Using the Air Genasi token for mist form I attempted to escape a Cave Bear. Though in mist form instead of the 100% miss chance, the bear hit me twice. This was tested with Jaydemoon using potions instead of the token, and we duplicated the bug. It seems that the 100% miss chance doesn't always apply.
A player character cannot have more than 50% concealment, so unless this spell is somehow applying 100% miss chance upon the attacker (different things in nwn terms, miss/concealment), then it isn't really a bug but perhaps a documentation error.