My take on this, is that the engine should be shut down if anyone is
exiting the airplane for any reason. I think that "knowing" that the
prop is there isn't enough. People get distracted, hurried, etc.

This reminds me of a time when I was a kid and watched a friend of mine
stick his fingers into the prop swath of a model airplane. The prop cut
his finger to the bone. I asked him what happened, and he said "I guess
I just forgot it was there because I couldn't see it, and then just
reached in to adjust the idle screw"