I don't know the answer to this problem, but just had to comment that this is one of the greatest frustrations I've run into in quilting. My problem in my some of my earlier quilting was not watching my piecing closely enough and having the edges not stay lined up for the whole seam. Getting one piece of fabric off track a little bit can make for much too weak of a finished seam to hold up. Of course, it doesn't pop apart until after the quilt has been finished! Ugh.