I was trying to pick up and place an item (A) in my backup and accidentally dropped it over another item (B). Normally, that'd just swap the two items, however in this case item B disappeared -or- it may have moved out of reach. Item A was some matches and item B was a vitamin bottle, which is slightly larger. I've included a Twitch clip that shows the problem. I didn't notice at the time, but upon review today it looks like there *may* be a bottle inside the bookshelf, suggesting the item was merely swapped and teleported out of reach. You can see that it's not in the vicinity even while standing.

I was running DayZ Experimental 1.14.