I see said the blind man
So the consensus is that the spinning is occuring during the cast, and that a stout leader will resist spinning. Makes perfect sense! In fact maybe even adopting Mason or the more readily availble maxima or other quality leader would help that cause in addition to diameter.
I still respectfully maintain that root cause of the rotation is design, however if the popper is working and catching fish it ain't broke don't fix it and understanding the role of the leader is key. It's common to change a magic fly/popper and lose all the mojo.
Something I hadn't thought about, and a good trick to have in the bag of tricks!