I am not certain with the PF-9, but the P-11 this is common and by design. Kel-tec calls it a slide STOP not slide release. I got in the habit after a reload of just pulling and releaseing the slide. Now, 2 years and about 400 rounds later, i can almost use the stop as a release. I would say staright out.. don't change it (although some have) use it as the manufacturer designed it.
Enjoy and good shooting.