Try giving it some gas just free rev the engine a bit, I have to do it on mine from time to time, I think it means the clutch isn't perfectly adjusted, but when I adjust it either it slips or doesn't disengage as well, so I just deal with it, but I'll just put a little pressure on the shifter and hit the throttle a little and it usually pops into neutral then, I believe it's because it isn't fully disengaged, but it's not engaged enough to handle the extra power, so it then slips so to speak
