I had the spring fall of the shifter mechanism inside the clutch side, and it stuck in the gear it was in and had to push the bike around dragging the tire. that was the 250. The 500 while in neutral, last year at the Polo hillclimb, I was warming it up and it screeched and lurched forward, while in neutral. It was neutral with the clutch pulled in, but stuck in gear at the neutral poistion. It was hung up and nothing to fix it except disassemble. The gear had seized on the shaft and needed to be pressed off. Apparently its staight gear to shaft, no bushing or bearring at all. Rare deal, but it happens. My engine builder said there was alot of goop in there, even though I change oil regularly, and that may have caused it.