I had an acquaintance who said that they were taught not to shoot at personnel with the fifties. They were supposed to shoot at their canteens or other hardware on their belts.
Urban legend based upon the myth that the Geneva Convention bans .50 cals for anti-personnel.
A most humane practice, I would say. A bg is probably easier to reason with after having a 50-caliber hole shot in his canteen... or something...