I've had it happen to me twice. I will refuse to promise to stop buying land as a principle, always. I never make it. And sometimes, later the AI will claim that I "broke my promise to not buy land". It is annoying, I consider it a bug because the AI explicitly says you "broke a promise" when you didn't make one. I understand that refusing also makes them mad, but the OP is talking about this case. When the AI claims you made promises you didn't. It only occurs with the request to stop purchasing land. Incidentally, you are also screwed if you promise not to acquire land because your cities will do it on their own. You fail and get the broken promise neg no matter what you do sometimes. When the bug occurs it never stops and recurs about every 50 turns.
I had a game with a neighbor that LOVED me and every 50 turns he would pop back up complaining about the broken promise that I never made. Later when there were no adjacent squares to acquire, ironically, it would even say I completed the promise (that I never made). when this happened the exact next turn the broken promise would reset as a bright red neg and he would pop back up complaining anew about the promise being broken. I watched this cycle happen about 5 times years after all the borders were set. It has to be a bug.
