I often put the border fabric on the bottom when I am sewing and never have wavy borders, I think it's all in the measuring and how off the quilt is befre you frame it. If I sew on the quilt side I can be extra careful about points that get chopped off.
I used to wash everything and so now I have about half washed and half not. It all goes together wonderfully, no problems either way. I also do not use starch and it's fine.