This is video of the shootout between Houston PD and a suspect back in January. I tried to cue it to 1:09 where you get to see one of the officers responding to the incoming fire and losing his gun’s magazine twice in the middle of shooting back.
I have seen that happen before at IDPA matches and I am going to hazard a guess and say the gun has an extended magazine release button. If you are shooting relaxed and without any stress, you will have a wicked fast mag change time. But if you are under adrenalin, a small shift of the grip and you are pushing the release accidentally and the mag disappears into the Oh Crap swamp.
I am not saying you cannot trick your gun; I am all for shaving a fraction of a second if that keeps you alive. But make sure the gun does not go Tango Uniform because of it. Suddenly having a short stick in a firefight sucks and is dangerous to your health.
Oh yes, carry a tourniquet.