I remove the paper before I sew sections together. I have never had a problem with distortion. There are lots of bias edges in PP but pre- treating the fabrics with starch and handling gently solves these issues.
When sewing seams on PP it is to hard to remove all the paper in intersections and has its own issues.
I have found ignoring the 'rule' about leaving the paper on till done is just not necessary in most cases.
peace