Sometimes in a game, after I make peace with someone, every turn after the peace treaty expires, I am informed that the peace treaty has expired. I've had this happen in a few games now.
This time, Alexander declares war on me and attacks my homeland. I fight him, defeat his invading forces and shortly after Alexander asks for peace, offering me a lump sum of gold and some gold per turn. I take his offer and peace ensues.
After the 10 turns of our peace treaty, I get the message on the right hand side that our peace treaty has expired. Then this happens the next turn, then the next turn, and so on.
In a previous game I countered this by declaring war on Bismark and then wiping him off the face of the Earth.
See attached game below. You might have to play a few turns before it happens.