Several guns do that, depending on how hard ya throw the mag in. SOme people actually WANT that feature. And, on other boards, I have seen some people upset that their newest gun (whatever it is) DOESN'T do that - they considered it a malfunction if it didn't do it.
I personally don't want the slide to close on its own, and most guns don't unless U really slam it home.
But, if that is all it is, I would still use it for carry. I don't typically carry an extra mag anyway (although, I have 11 rounds total in my P99c - if I had less, I might).
If U can go another 200 rounds w/o a jam, I'd say its fixed. I would carry it if thatw as the only issue with it.