I don't use the HB 500 c/m as much as I might, but recently, about every other roll is coming out of the film back backwards! I don't know why that is. I'm 99% sure I'm loading the film correctly. (I've even checked with several on-line videos). Am I overwinding the film after the 12th shot? That doesn't seem like it could be. Does anyone ever have this problem? thanks!