Happened to me as well. In two cases already.

First I ran into electro and punched a guy in the head from the back... who was also in a firefight. As a result, the other dudes killed him, and I managed to take his loot. I ran away madly with the full awesome gear, just to see it all disappear a minute later. (the dudes who killed him went for the loot)

What is interesting in this case is that I actually changed my shirt and pants, but as the items disappeared, I gained my original (starting) equipment back.

The second case happened just recently: I followed a starter guy, who ran to pick up his corpse. (he fell off from a roof or something) Same way, I went there and punched him properly, he gets knocked out, and I take his only weapon, a fireaxe. 15 seconds later, the fireaxe disappears. (He looted it from the dead body again.)

The interesting thing in this one is that I actually didn't loot the item from the dead body; it was from a living player. Thus any object gained through looting a dead body have this glitch, no matter the fact that it was already passed through looting to another player. (But it wasn't dropped to the ground, so maybe that would help..)

I also wish to note that I didn't actually moved the items to a slot in my inventory: I grabbed the whole bag, pants, weapons to my character. Probably, if you drag it INTO your inventory, say you find a nice axe and you drag it INTO your bag, it would be a different scenario. Probably. This should be tested properly.

And yes this probably only annoying in intensive situations where you don't have time to hide the body, and someone else might mess with it.