I get this a lot also, usually because I hit "X" on gamepad for an ability just a split second before pulling the trigger. What I would suggest is to try the setting for Toggle crossbar instead of pull/hold. I havent tried it though so it may be a pain since you are using dpad up/down to select party members, you would have to toggle off everytime you need to change target. Best solution would be like you suggest, disable the menu during combat...