Ugh, I hate it when that happens. I quilted a pleat in the back of my Karyukai quilt but it was my quilt so I just left it. But since then I have gotten into the habit of checking well and giving my backing fabric a good strong tug on both sides with every advance before attaching the side clamps. Then I look again to make sure I have no ripples. Amazing how a situation like this makes you form new habits!