I have never had one go bad, but when I pour a smaller jig like a 1 oz for several hours, the mold does expand some, and I either get flash, or the jig gets stuck in the mold. So what I believe is happening, is either the mold is warping a bit (thus the flash) or the cavity expands and contracts too fast, thus not releasing my jig. However this is my first time pouring 2 oz and 3 oz baits.