Demon Hyena bug

I encounterd a bug while i was fighting against the demon hyena in act II. After beginning of combat, i ran down to the lower level on fighting the hyena demon while killing the minion hyenas spawning. The demon followed but stopped fighting and went back to the upper level in anticipation like at the beginning. Went to him and fought him, but he didn't respond and didn't fight back. just stun locked, his live points didn't change too. I went down to the lower level and fought about 100 spawning hyenas but killing them was an eternal loop. They did not bring experience points. Therefore this bug isn't exploidable. I had to sacrifice myself to the hyenas to set the area back.

Hope this helps :) awesome game!