It's a bleed through effect to your ships manouvering thrusters, when it happens and you are lined up on a particular level, say the orbit line so it's horizontal, when you exit the FSS it will be out of line. it only happens sometimes so I can manage, sometimes moving closer to the object being scanned helps, it doesn't happen every time but it's obviously of low priority. The FSS spins because your ship is spinning, you can use the same actions in reverse to stop the FSS spinning just as you would to stabilise your ship in space. A lot of the effect also depends on what controller you are using for the FSS, some are easier to use than others when this happens.