An empty mag follower will push up the slide stop. This is what causes the slide to lock back when the mag is empty. If you have the slide locked back and an empty mag inserted it is still pushing up the slide stop. Just pulling it back will not unlock it. Put a bullet in the mag and the follower will not be pushing up the slide stop and just pulling back the slide will allow the little spring on the frame to push the slide stop down and allow the slide to close. Dan