"Ahn'kahet: The Old Kingdom"s last boss bug

I had a quest to do in the dungeon mentioned above....went through the whole instance and it was all fine until i got to the last boss , when casting Insanity , it just stops but keep doing that spell's animation.... nothing else happens afterwards , even when u leave the instance and enter again , it's always the same issue .
Hope you fix it soon , because when i asked in the Global chat they told me it was working last week, and i found out about this bug 4 days ago.

Well, we are able to get the achievement now because we can kill the boss.
The boss casts Insanity but nobody gets infected and we just keep fighting like we're going against a normal mob. meh....

5 mans are getting more and more bugged over time, nothing new...
ToC 5 can't be done, because the chest after 1st encounter doesn't spawn. And now this ****. Also VH is a one big mess...