Most likely culprit - sideways force. Inadvertently pushing the wood to the side, usually while making a turn. This bows the blade since both the top and the bottom are held in a straight line. Once you get a piece out, check that the sides are really straight with a good straight edge. This is my biggest problem with the scroll saw and I am constantly fighting it. I've taken to completely releasing the wood every 5 seconds or so to make sure I'm not pushing one side or the other. Unfortunately I don't have the automatic indicator that my wife and kids have - sticking my tongue out when I'm concentrating too hard.