is just there to help the spring locate and secure the stop in the up position. You push down and it overrides the spring pressure and locks the slide in the slot. When it is pulled to the rear there is a ramp (as mentioned earlier) that pushes the stop up and the spring pressure holds it up until you decide to again lock it. It won't fall out or come out because even when the slide is dismounted, the spring holds it. It is a wonderful engineering solution that eliminated a part and works well. The entire slide stop/ramp design is just a beautiful piece of design work.
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