I'm not happy about joining the club but I finally did it. I put a blade in upside down. I blame it all on Pegas. I had used F/D blades and they have the little dimple ground into the top of them. So, I just got a gross of Pegas MG blades and they have marked the ends of theirs with a tiny, well I don't know what you would call it, but it denotes one end from the other. I assumed, and that is where I screwed up, that the marked end was the UP and the plain end would be down. I couldn't figure out why my pattern was lifting along the cut line. The blade was cutting fine because it is a reverse blade. So, I didn't realize at first what was happening. I finally had the "uh huh" moment and saw what was going on. So, a word to the wise if you use Pegas blades. They are marked but the opposite of the F/D blades. Dang!!!