Freeciv

AI diplomacy countdown values < -1 are supposed to be war stubbornness, meaning that players are at war and do not accept ceasefire until countdown value reach -1.

The countdown is correctly set to such values when a war is declared, and it's being updated each turn, but I don't see it being consulted anywhere when considering ceasefire, either direction (proposing one, or accepting one)
I suspect this leads also to secondary problems, as after such a ceasefire is accepted, the AI diplomacy is in illegal state of players not being in war + the countdown indicating that they are.