I have seen this bug with pens, matchboxes, empty water bottles, various hats, bandages, chem lights, knives, crowbars, ammo, food, etc. Items I haven't seen this bug with are backpacks and other more rare items such as firearms.
Perhaps my most notable experience with this glitch is when I found 6 batteries on top of each other or the time I found 3 sardine cans together pretending to be one item.