Actually this happened to me when I was quilting a customers quilt. What had happened is that all of the threads weren't clipped on the top and one was 'looped' in the seam and the foot caught the thread and since LA's run so fast, it created a hole with all the thread that had to be cut and picked out. I did tell her about it and offer to repair, but she said she'd take care of it. So sometimes even though everything looks okay, trouble may be only a small thread in a seam away. And yes she should have at the very least told you!