I defense of SH2pilot, it is possible (under rare conditions) for a slide stop to be correctly installed and to pop out during firing. It happened to me.
I won't name the brand, because the model has long since been discontinued, but a number of years ago I borrowed an Officers ACP size pistol (by a manufacturer other than Colt) and I was shooting it at the range. I probably put a couple of hundred rounds through it and didn't notice anything amiss. Being right-handed, when I put the gun down on the bench the grip was always to the right, with the slide stop underneath the receiver.
I let a friend try the gun. The friend happens to be a lefty, so when he put the gun down the slide stop was facing up. One of us (I don't remember which) happened to look down at the gun and said "What the ...?"
The slide stop was partially back out of the receiver. That explained why the slide hadn't been locking back on empty. The question was -- how did it happen? We reinstalled the slide stop, fired a few more magazines through it, and the same thing happened. Mystery.
Mystery solved: Close examination of the slide stop show a lot of brass staining on the underside of the slide stop lug -- the part that engages the magazine follower to lock the slide open with empty. What was happening was that the last or next-to-last round in each magazine was moving forward slightly under recoil and making contact with the slide stop lug. This is a known problem with weak magazine springs combined with slide stips that are marginally out-of-spec -- but neither of us had ever seen it punch the slide stop out of the pistol. Usually it causes a stoppage.
BUT ... this was a short 1911, a 3-1/2" barrel. The timing on a short-barrel 1911 is different from a Government model. And if you look at enough 1911s, you see that there are variations in where some manufacturers locate the slide stop notch in the slide. Apparently, all these variables combined to produce a pistol in which the bullet managed to hit the slide stop at the exact moment the take-down notch in the slide was perfectly aligned to allow the slide stop to come out. A bit of judicious adjustment of the slide stop lug with a small file, and all was well in Dogpatch.
It can happen -- but it's extremely rare.