1. "Tex" deserves creidt for posting this.
2. The Serpa does create an unsafe condition. There are many who use this holster and train intensly with it, under stress. There are many more who draw only with an unloaded gun, or (relativly) slowly. The ND's seem to happen under high stress, as in this case.
If, as noted, this was the last 'take' of the day, Tex was probably going as fast as possible. A minor glitch in the draw resulted in a 'clutch' response - using more force than needed. I have been in situations where I have done the same - tried to overpower the system (though not on a draw - yet).
There is another posting on the net of a gent who said he was being robbed ( a high stress situation), went to draw from a Serpa, and shot himself in the foot. He includes pictures of the hole in his shoe and foot. The bad guys ran off at the sound of the shot.
The Serpa is the only holster cited by name in several ND's. I do not use one, and will not allow one on my ranges.