Hmmm. I wasn't holding the thread tails. Usually if they are long I have less of a problem, but your comments helped me realize this was happening on the last project, too...which was why I dusted off the Pfaff 6074 to finish. I think I will have to do some fine searching w a flashlight in the bobbin area...perhaps some thread stuck deep. What is a leader? And will it work with starting a seam that splits a corner? Thanks.