We've had about 4 NDs into the leg with Serpas around here. Also, I have seen both newbies and experienced officers have to fight the holster for a draw at times.
A regional IDPA director says there has been significant discussion of banning from the sport. It may not be politically correct to do so as they are duty holsters for participating LEOs. They do have an affordance that leads to an ND. Such factors under stress can negate even lots of practice.