The zero stop for the turret is not set properly. It'll engage targets and will shoot the player's plane depending on the angle between the plane and the target.
Not too difficult to reproduce, simply fly by a target (either ground or air) where the turret will have to aim down in relation to the plane. This mostly happens when the target is in front of the aircraft but will occasionally happen when the targets are at 090°/270° or further to the rear. The easiest way to avoid it is to fly at 90° to the ground when flying above ground targets.