Hi,
A good friend of mine (a quilting judge) told me that after safety pinning my quilt sandwich and I'm ready to SITD use straight pins and pin across the seam. It will keep both top and bottom of quilt from shifting. I do this with my domestic machine and I put them in as I am sewing (about 7 to 9 pins) and them take them out and repin as I go. It has really worked for me. Hope this makes sense.
Juyd