I think Dan hit the nail on the head. The retention spring pushes down on the arrow about five inches up from the nock so if the arrow or rail is straight then it should hold it down flat regardless of how hard it pushes. I would first check the arrows to make sure they are not bent. Give the a roll on the table and make sure they do not wobble at all. Then maybe check the rail for anything in it. Can you see it lifted up and then take a knife and lift up on the tab? What happens if you do this? I would start with the arrows.