[Bug]Rearrangement of gym pokemon?

Me and my friend went out the other day to take gyms down together and every time we would attack it and go back to attack it again our pokemon would be arranged in a random order in the gym selection. Very annoying to rearrange. It wasn't even in any specific order either. (Our highest cp pokemon wouldn't be first it would be a random one) is there any known reason and or fix?