I think what happens is that if you drag an item into the vicinity, it can somehow appear on top of the object behind you. In this case, it probably disappeared from view and the vicinity list because it ended up at the top of tall furniture.
A similar but worse issue can happen where if you drag an item into the vicinity, it can get stuck inside the furniture behind you. For example, a gun will be partially visible but attached, passing through or fused with a bookcase or shelving unit. It won't appear in the vicinity and targeting the item will not be possible from any angle, thus the item is completely lost.