That can happen with any semi-auto pistol. After a shot is fired, as the slide is traveling rearward with the extractor pulling the spent casing out of the chamber, the top round in the magazine or the nose of the follower and feed lips of the empty magazine provides support to the spent casing to keep it from sliding too far down the breech face. If there's no magazine in place, the gun may fail to eject or even eject a spent casing down the magazine well.