The problem is that the slugs get canted a bit when the sail comes down. They are just a bit smaller than the slot in the mast (the next size up is too big and the next size down is way too small). When the slugs get canted they jam. It actually happens both ways, but going up, you just release halyard tension and let the sail down an inch or so to get things going again. You can do the same on lowering, but that takes longer than just pulling the sail down by hand. I am certain that a downhaul would just jam everything up near the top of the mast since it would pull down on the head of the sail