When I play the middle B sometimes it plays the G above the staff. It doesn't do it when I first start playing but after I have been playing for a while? Is this related to moisture? I have trouble with the C too. It doesn't want to play.

its because your over blowing the note, probably your emboucher is too tight, my teacher made me try to get to the G from that B, was kinda hard because I was used to just playing the B

I'm beginning to think it's my fingers not covering the holes because if I play those notes carfully making sure the hole are covered I don't have this problem. However if I'm playing somthing and not concentrating on finger placement I get sloppy and then the problem. It only happens on the the long B and C though.