You explained to Sutech why this problem remains, I just want to say that I think this should be really on top of your to-do list: it´s a bug that can be exploited easily and which seriously threatens the gameplay!
Why? Because it happens very often and changes the game very much! For example, in the game "Anachronism", I had control over Denmark for a long time. Then I moved out of it, retaining control since no one moved in. Next turn, I tried to move in again, Russia did the same, and we bounced - turning Denmark neutral which cost me one built.
In the same game, there are currently three situations (Brest, Serbia and Rumania) where an attacker could simply turn the territory neutral without winning the battle! And if I look at my other games, there are even more situations like that - in fact, it´s a quite common strategy to move out of your centers and defend it by moving in again.