Game Mechanics: Losing Stacked items

[Lumpus]

In addition, if you then go to a vendor and sell the stack of one item, the item does not disappear from your inventory. If you attempt to sell it again, you get stuck at the vendor and can't do anything (except jump apparently, which i just read about).

If instead of trying to sell the item a second time, you drop it on the ground instead you get an error indicating that the item couldn't be located in a particular bag slot, and it then poofs from your inventory.