The violent recoil of the "straight-blow-back" Pocket 9 often caused the slide stop to jump up when it wasn't supposed to. After seeking many solutions, the thing was just disabled in order to solve the problem. (Count your rounds!)
Originally it was like the slide stop on a Walther PPK, i.e. it was both an ejector and a slide stop.
Several designers worked on the Pocket 9 over the years. One from Israel, one from Brno Cz, etc. Each had his own ideas on what would make the little critter work. Thus, it changed over the few years of it's life.
The aluminum grips were the best, for several reasons... They didn't break! And they added weight to gun, which helped with the violent recoil.