I quilted an entire wide border on a queen sized quilt for a customer before I decided I didn't like the way it looked...8 hours of frogging perfectly tensioned quilting was a bummer but I hated the thought of quilting that FMQ pattern on 3 more borders. I hate it when the center of the backing sags or one side sags...ugh! I have gotten into the habit of checking the backing after every roll...never had a tuck like you describe, but that is only because I check every time. I am so sorry you had this happen...frustrating to say the least!!!