I encountered another Great Mage, set my forces up to capture his conveniently located and underdefended capital city, and then took it in one turn. After his faction was eliminated (I got the eliminated screen), a demand from him popped up, with both both the accept and decline options grayed out. I hit escape and went on. It reappeared next turn. And kept reappearing. And won't go away. I finally just abandoned the game.
This is a nasty bug. Please fix it.
This is a nasty bug. Please fix it.