Today I was playing priest and got a mistress of pain from a piloted shredder. I had an auchenai soul priest and lightwarden on board. I hit the opposing hero with the mistress of pain. and i kept getting repeated damage to my hero untill i died. I couldnt record the original incident, so i recreated the situation using cabal shadow priest, and the same thing happened.
It's not a bug, it works as intended. Every time when Mistress deals damage to whomever, she heals your hero. Auchenai converts all healing you do to damage, and since Mistress unintentionally tries to heal you with damage (she does end up damaging your hero), you end up being dead. Yeah, it's fun, isn't it?