I don't have any information regarding which ones cup. But I have observed it in my own seedlings and more importantly confirmed to me by Kevin Vaughn that cupping is indeed a problem.
I would be surprised if Margo-no-Sakura was tetraploid. That one sets a pod for every flower without my help. Perhaps I will take a closer look this year at the seeds within these pods. Last year I just tossed them during clean up.