Yesterday I was with a friend that was shooting his brand new Rock. The slide released from being locked back when a new full mag was inserted, the release lever was not pressed. My Rock doesn’t do this. Is this a safety issue?
It should not do that. Have you been able to duplicate it? If you try, use snap caps
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Slides will often release when a loaded magazine is forcefully inserted in a semi-automatic pistol. The action is not designed to occur, but it is also not a flaw in the pistol; it is simply a matter of physics.
Nearly all pistol magazines are tilted slightly forward in relation to the top of the pistol’s frame and the axis of slide movement. Forcefully inserting a loaded (hence, heavy) magazine into a pistol pushes the pistol frame forward a small amount. Inertia keeps the slide from moving forward as quickly as the pistol frame. If the frame moves forward enough before the slide starts moving, the slide lock may drop and the slide will be released to go into battery.
S&W M&P pistols were notorious for “auto forwarding” when mags were inserted with any degree of force. M&P 2.0 models had an extra latch added to the slide lever to prevent auto-forwarding. While the slide releasing with mag insertion is most prevalent with heavy mags, light frames and heavy slides, it can be induced in any pistol if enough forward force is applied to the frame.
Below is a video of an H&K P30L auto-forwarding when a 17-round mag is slammed into the gun.
https://www.youtube.com/shorts/5eajxPfr0dY
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It’s sometimes called a “Kinetic Slide Drop/Release” and is not entirely uncommon, especially when forcefully inserting a magazine. It’s not indicative of a malfunction in the pistol or a design failure. It is also not generally considered a problem or a safety issue. Some people consider it an advantage, actually.
Anyway, it’s not anything to worry about and it happens sometimes.
Peace favor your sword,
Kirk
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As Kirk sez: “It’s not a Bug - It’s a FEATURE!” 
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I guess my friend is one lucky dog then. He didn’t have to pay extra for this “FEATURE.”
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Definitely not something I’d dismiss as a “feature”. As mentioned above, try and reproduce it with snaps. If it’s reproducible, best to be safe and pursue through customer service.
Try inserting a mag just using thumb pressure till the mag locks, with snap caps or if at the range live ammo. Then give it a more forceful attempt and see if the slide goes into battery by itself. You may find it is just the forceful mag insertion that knocks the slide off the lock. Remember Safety 3rd.
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