During stress test 31 I have come across a bug where magazines get stuck in the weapon and will not function. First it happened on an AKM. I looted the AK empty and later found a clip. When I opened my inventory to find the clip (and fill it with rounds) it was already attached to the weapon, so it had apparently auto-attached itself, which I am not aware if it is intended behaviour or not. The mag could not be removed from the AK in any way, and on the character the AK was still visually displayed as without mag although the AK's inventory showed a mag with 12 rounds in it.
I could cycle the mechanism with R to get rounds out of the mag, but the AK would not fire until I had emptied the mag of rounds with R and chambered the weapon manually. At no time could the mag be removed.
It also happened with my Makarov. I had earlier found a Makarov without mag that I had saved in my backpack. Later I found a new Makarov, this one with a mag with six rounds in it. I went to throw away the earlier Makarov and noticed in its inventory that it now showed a mag with six rounds in it that could not be removed!
Another strange thing is that after the mags got stuck I could no longer aim down sights, middle mouse or shift did nothing with raised weapon. It worked before I tried removing a mag from the weapons, but not after. Relogging fixed this but did not affect the mags.
Sadly I never found a second mag for either weapon so I could try to "unlock" it by swapping mag. Both weapons were rendered useless by the bug, so I'd classify this as a serious bug.