I just finished a game where I conquered a city from Magnar and some time later, Kraxis declared war on me and subverted the city that I took from Magnar. I figured that since I had an army right next to the city I'd take it back. I walked in and took the city without a fight, set up a build queue, and then I couldn't do anything else. I couldn't move my armies, I couldn't end the turn, nothing. the game was stuck.

I reloaded to the last autosave and the same thing happened again. Eventually I just ignored the city that I lost and won by Spell of Mastery but it was irritating and would have prevented a conquest win.