REV, maybe it shouldn't matter but I have a 1911 with a Novak 8-round magazine who's slide stop will not release on an empty magazine with all the force my thumb can apply. :)
I have two SR9s and neither exhibit the problem, even on an empty magazine. My LGS is operated by my nephew so when...
Are you trying to use the stop lever with an empty magazine inserted? On many pistols it is more difficult to release the slide with an empty magazine.