I've noticed this before. It happens when I claim corpses. It shows up in the default client as well.

- Invisible Items.jpg (9.24 KiB) Viewed 3420 times
This is a picture of some of the other invisible items, but was taken in the default client.
It was not until this year that I saw other invisible items besides the "unused" item. This is "Short Beard" and a "Ponytail" on the ground.
Here are the names of the items that my trasher found in my backpack and then attempted to throw away.
- Short Beard
- Goatee
- Ponytail
- Long Hair
- Mustache
- Long Beard
- Unused
There are other unnamed items as well. They all appear to have unique graphics. I don't need the graphics since I can filter by properties.
I went to investigate, because it annoyed me seeing the "you cannot pick up this item" message popping up every second or so. Then it confused me why I was seeing Beard and Hair stuff (printing out the properties). It looks like it is a finite list though (not randomly named). The only one that is visible is the "Unused" one y'all showed a picture of.
You won't see any of these if you don't claim corpses in the Halloween Dungeon and even if you do get them in your backpack, they will eventually disappear. I have found no ways to remove them, but you don't really need to.