yeah most likely your thumb is pushing it...i saw my friend doing the same thing to my p99 when he shot it, the problem is with the slide lock it is not like standard HK's sigs, etc. where it goes up, this one is more of a button you push inside vs slide down like 1911's.Are there any known issues with the P99 AS not locking the slide back on the last round being fired and ejected? What are the usual things to check? Mags are in excellent condition and not old. My guess is I was riding the slide release today with my right thumb causing it to do this with every mag I had with me, but I want to eliminate other possibilities too. I just noticed that my right thumb lays on the release in my usual two hand grip with my thumbs pointed toward the target.