doxiemom11 pretty much hit the nail on the head. There is a tab with a single screw holding it in place at the middle of the top of the door on the inside. When that breaks or the screw backs itself out, the door will slide forward and backwards even at a stand still. When you open or close the door, the piston will help slide it in one direction or the other.
Open the door to the point that there is not pressure on the piston and gently tap the door in the direction with the palm of your hand. Then replace the screw or tab.
