He was tethered to his boat. I'm speculating he was wearing a PFD with integrated harness. It appears everything worked like it should -- once. But the second time his PFD/harness was pulled off of him.

A PFD/harness design or manufacturing problem? Did a clip/strap/other part break or come undone? Was the design such that under the right conditions it could slip off over one's head (e.g., no crotch strap) or be pulled down over one's feet?

User error? (e.g., PFD/harness worn too loosely)

I've heard that a harness with no crotch strap that is too loose can be pulled off over one's head. Has anyone ever heard of a harness being pulled off downwards over one's feet? The reason I ask is that the sailor lost all of his clothes except for his shirt. That could have been the result of two different causes -- PFD/harness failed or slipped over his head and water turbulence pulled off his clothes. But could his PFD/harness have been pulled downward, stripping off his lower clothing in the process?