Well then....My SIG has not locked back several times already. I have 2,000 rounds through it. Last range trip it happened once. Before that twice. And....weird...I think its a magazine.
But what else could it be?
could be magazine, too strong recoil spring, low power ammo, dirty slide release, worn slide locking slot ... easy to eliminate magazine - mark the one that does it so next time you know if it is the same one or different one.
To OP - as most already said, glocks do that but I wouldn't count on it as a "feature", proper way to release slide is to hit the slide release. but you not hurtin anything either :-)