I used to have a Netflix account way, way back when the just rented out discs. A friend and I would share movies we rented. There were no problems at all returning discs through the USPS from my home, but whenever he returned movies near him, they would disappear.
Few people are blaming Shou in this- fault looks to be with the USPS, whether theft, carelessness, or whatever caused labels to be switched around.