I didn't see anything in the forums on this, after looking 4 pages in so I apologize if it's been brought up.

An Ai faction declared war on me and I took one of his cities. Apparently this riled up the enemy Sov because he led an equal combat rated force right to the newly conquered city, now my territory.

After wiping the pavement with his face, his entire empire (7 cities) disappeared. OK that's fine except I can't build a city anywhere one of his cities were. Map Tile still claims it is a city square. So between Mountains, hills, swamps, forests and now invisible cities the southern half of the continent is uninhabitable. Minus that one square Another AI Faction decided to colonize and is stuck in because he can't build buildings to expand the settlement.

Is this normal?