Unable to target Cursed King in Dark Forest Map

He appears to be doing all his normal attacks, but I am unable to target him. Furthermore, none of my minions appear to target him. Mousing over him makes no difference; it's like he's part of the scenery.

It's the ultimate defense, haha. But it killed this map for me. He is immortal, and I am unable to leave his arena while he lives.

I've done the map and boss successfully in the past. I'll post again if I'm able to duplicate the problem. (Others should do so as well.)

Oh, and this was a tier 8 legacy (square) map. I assume that is not relevant, but you never know, so I'm mentioning it.

Does this occur in all phases? Or just in one particular phase (wolf-spray, wolf-shape-shifted, etc.)?

All phases. I never had any chance whatsoever to do damage to him.