GEAR: MP-133 with pistol grip in hands, long rifle (Winchester) on back, Shock Baton on melee slot. Can't remember the type of backpack, it was blue/white and had 20 slots. It was full of stuff.

Crouch down (did not test it upright), tab the gear open, DO NOT set shotgun into vicinity manually, just keep it as is in hands. Select can of Pipsi from backpack, click on DRINK. Shotgun disappears from hands, replaced by seemingly unopened can of Pipsi. At the same time you see and hear animation and sound of drinking. After sound and animation stops, you still have "unopened can" of Pipsi in your hands. You cannot remove it, you cannot drop it into vicinity. You also cannot see your shotgun anywhere nearby nor in your hands.

Solution:
Relogging into the same server fixed it. Consumed can was now gone, "previously lost" MP-133 with handgrip was back in my hands.
I repeated it twice. Both times same issue.

Testing:
I had nothing else but various "use once" Pipsi cans to try with, I wanted but could not find at the time water bottle which I could have tested with incremental "DRINK" and "DRINK ALL".

I tried instead consuming Rice (EAT, not EAT ALL). Since I had less food to play with, I could not allow myself to test "EAT ALL" option to see if it differed. But with incremental "EAT" shotgun was put properly to the ground each time and visibly returned into hands after consumption of Rice was finished.

Did not test with different weapons.