Invisibility potions are not effecting how mobs perceive the player. What I mean by that is, they can still see you when you are under the Invisibility effect.
I went ahead and tested this in 1.5.2 and 1.6.1. In the 1.6 update, I was being bombarded by zombies and skeletons that somehow got their hands on thermal goggles. In 1.5, I was practically jumping in their faces.
Please fix this soon. This will effect adventure maps that use invisibility potions to quickly move past enemies, instead of confronting them.