Well my dads 05 900 poo decided for the whole seat to fall off the sled. We were only going 20 miles an hour down the side of a road, and he hit about a 3 foot snowbank and the whole seat fell off. Soo, its now in for repair. Get this, the seat was only held onto by 2 screws and an attachment for the back lights. Must be the vibration causing it to come loose.

Happened to me also right after the dealer did the tank up date a few year back. Had to pull off my hand gaurds so I could use the bolts to reinstall seat. If I was you I would also put some blue lock tight also on bolts.