@Riot, Anivia question

It seems that it's treated like a channeled ability. Any sort of CC will interrupt it, just like Katarina's ult can be interrupted.

Even if this is the case, I do think that Anivia could use a buff and a change to this Zhonya's interaction would be nice.

I think its because the attack continuously drains mana. Zhonya's is designed to prevent ALL status and health changes (mana included) so it cancels any ongoing mana drains (ie, her ult).

This is my guess/inference, though. Not completely sure.