Milos, does this happen in all battles, or just occasionally? Either way it does seem like a bug. In fact, this is probably the same as one we encountered during testing, but were never able to figure out the break in the combat timing logic.
Also, I need to say publicly that, while I understand why you and your brother are doing what you're doing, and I understand that this is a pretty common practice, I can't condone it if you are playing the game simultaneously, as you are then in effect using two copies of the game, for the cost of one. If you are never playing at the same time, then technically you're still just using one copy. But if you are playing concurrently, I hope you will consider purchasing a second license, if and when you are able.