Sometimes when I shift it won't shift, and when I press it again it shifts down/up two gears at once.. Is there a reason this happens? I just got a new rear cluster, could this be the reason? It doesn't happen all that often but it does getting annoying.. I'll shift and think it changed gears to see it really didn't, click it again and it'll switch two, then i'll have to downshift to get to the gear I wanted.