Fungus Mutant stun
 

When affected by the Fungus Mutant's stun when he hits you with a melee attack, 9 times out of 10, all spells will be interrupted until you die after the stun wears off.

You can try to cast spells, and they will start to cast, but then they simply stop. No message about the spell being interrupted or anything. It is almost as if the stun lasts twice as long on the server-side as the client-side.

I have died 7 times from this now, so it is easily reproducible.