I can confirm that the bug is still present in 1.6.2 pre and release.
Bug still exists in 1.6.1 release. Ghasts don't see through invisibility, but all regular hostile mobs with the new AI, (spiders, skeletons, creepers), do.
Kind of annoying, since I brewed an full chest of invisibility potions.
It's only been on the 'popular issues' page for a week, hopefully someone will get it fixed soon.