On the bright side, it makes me feel better about my own pedantic streak to see it exceeded by another.
I believe that coin holder design is deficient, not having a "gasket" which is intended to keep the coin from moving in the "slab". The older PCGS "rattler slabs" were notorious for having coins that moved relatively freely in their housing, often generating a rattling sound when handled.
Mine rotate inside Whiman plastic 2x2's while sitting in a blue plastic Whitman storage box in a drawer. There must be a small amount of vibration in the drawer. And when I look a week later some have moved 30-45 degrees. Rotation inside the mail truck is a lot easier to understand.