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

[Thebrotha]

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.

[Thebrotha]

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....

[fanf3]

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...