I'm having this problem also. Even worse, I'm having a strange problem where when I move my sov alone or with his army I'll see the square light up where I told him to move, but before he completes his movement this square randomly changes to another square which could be anywhere on the map and starts heading there, making him impossible to move reliably, and grinding my most recent attempt to play this 'game' to a halt.

Also, whenever he attacks anything on the strategic map, his movement will be set to zero after the tactical battle, regardless of how many moves he had left when he started the attack.