Use pin through both seams and allow it to stand straight up. Then pin as usual before the seams and after the seams. Before and after will have less bulk. Then while stitching, remove the standing pin as you approach it. There is a fork pin (for lack of the correct term) available to quilters. This pin had two thongs side-by-side that straddle the seam.
I think by turning the pin to secure the pin, the seams are distorted. -- Hope this helps.