That's very strange. Looking into it right now.
Edit: Does this continuously happen, or in one particular battle? I've just tried it and it fires just fine. The fact that it spams "Firing!" leads me to believe that your vehicle was out of ammo or was otherwise unable to fire (broken gun?); firing should only be logged when it's actually fired, that is if the crosshairs are dead center on the target and we can hit it.