I just wanted to say that I have never done a quilt with prarie points on the border but my galfriend did and she had issues with the points wanting to slip and move.
I am just wondering if in fact the prarie points and attachment are not the real issue. The points and border are a LOT of fabric to sew through and I thought perhaps the problem MAY have started there. By the way, you have done a TERRIFIC job, anyone would love to have a quilt so lovely. If I am off base....sorry. If it can be distorted I have done it.............just a thought.