One other possibility is if the scope is not quite vertical in the mount or in your hold. In other words, if the scope is mounted with the crosshairs slightly tilted the adjustments will move in both axis as an adjustment is made due to the angle. This can also happen if the gun is not held exactly vertical when shot. I have noticed similar errors on paper when my target frame was slightly leaning and I lined up the vertical cross hairwith the target and caused a non vertical alignment of the gun and scope. If you lean to the left or rightthe shot will not hit where you are aiming. This can also happen when shooting on a hill or other unlevel ground due to our tendency to want theigs to line up, kind of an optical illusion that makes you think it is not level. This is why many target shooters use a level mounted on the gun that can be seen when looking through the sights.