I just bought a new bike, and the seatpost terminates in a sort of hook, with the saddle resting on the flat part of the hook in a little carrier. No matter how hard I tighten the bolt holding the carrier in place, I end up out riding and I'll hit a bump or something and the nose of my saddle will rocket into my crotch. This makes the bike very uncomfortable to ride if I'm not carrying a tool to fix it, and it seems like I shouldn't be having this problem. Is this a known bad design? Should I shim it with a little piece of tube rubber or something? Should I take it back to the shop and ask for a different post?