Today when I was riding, (this is the only time it has ever happened) I was accelerating hard, WOT. I shifted to 2nd very quickly and got back on WOT. It held for a second or two then POP and it went into neutral and hit the rev limiter. This was the first time this has EVER happened. It didn't do it the rest of the ride. Should I be concerned? Or did it just slip out of gear?