Fighting with an ally (but not in a coalition) and some units start fighting each other

I am in a battle and another player and we did not want to declare a coalition this early in the game. We had been fighting together on land and on sea against a common enemy without any problems. Then we used our subs to attack a cruiser (third time we had done this) and when the cruiser was destroyed our subs started fighting each other. No other units on land started fighting and we did not go to war. We tried declaring war and then peace again but could not get them to stop fighting. When we stopped playing for the night, we were at peace and the subs were mostly dead. When we looked this morning, two of our land units have started battling each other and every time they do, we automatically declare war. We continue to try cease fire and peace but they continue to fight. We cannot get them to break away since they are in an active battle. We have other units close to each other that are not fighting. We are assuming this is a bug unless there is some specially espionage that I have not seen that would cause this.

Please help!

Thanks.