I have been paper piecing for a long time , and could not figure out why the same thing was happening... Then it hit me, after re-sewing on the original stitching line after the papers had been taken out..... Its the paper... the stitching is laying on the paper and not getting the tension on the fabric... so once the paper is removed there is loose tension. How to fix this problem..... a few things to try, increase the tension, or once you have trimmed those outer units remove the paper then join the units, or use thinner paper ( think cheap newsprint) so the stitches can get better tension on the fabric. I also found that I was ever so slightly stretching my thread as I was pressing my units. When I leave the paper in and press ( and I love my steam) the thread when I use heat and steam stretched to accomidate the thickness of the paper, so once all the papers are removed and the thickness on the paper is gone... the stitched thread stretched and is not the correct tension.
I figured some of this out when I used "real" paper piecing paper , its thinner compared to the cheap copy paper I was using.
I feel your issue on this matter, you finally get perfect points only to get your thread showing... frustrating.
Last edited by Lori S; 03-24-2014 at 07:23 AM.