Peckish is right on target about the leaders and enders to stop the problem. I like to use them to save thread mostly-but would also eliminate your problem. I do not have automatic thread cutting but I know I would not like it if it only left an inch of bobbin thread. You need to be able to hold on to it. You can do that by pulling up the thread at the beginning of the line of stitching or just holding it while you do your lock stitch.