I'm in a war against Cyrus. I've more than double the points of the next civ, and just gotten Cyrus to Capitulate. Pacal used to be a vassal of Cyrus, but since broke free. At the end of the war, Mutal was suddenly under my control, with no units in it, and no announcement.
Mutal has 2 civs between it and myself, and was at the time the Capital. I didn't have any units on explore to take it over if it had no defenders, and I wasn't at war with Pacal.
Here's a screenshot of the city under my control with no units in it. Just randomly came up asking what to build in this city.
Cyrus was up to the left a bit more, below Justinian (grey) and Charlemagne (other Yellow).
Mutal has 2 civs between it and myself, and was at the time the Capital. I didn't have any units on explore to take it over if it had no defenders, and I wasn't at war with Pacal.
Here's a screenshot of the city under my control with no units in it. Just randomly came up asking what to build in this city.
Cyrus was up to the left a bit more, below Justinian (grey) and Charlemagne (other Yellow).