If you are in the process of sawing a log into boards, and you attach a board to your cursor and right click the ground to switch to stockpile mode, when your inventory is full it will attach a second board to your cursor.
If you are using a client which allows you to hide the cursor-attached object, you can then place a stockpile with the first board, but the second board is then permanently affixed to your cursor, and you can not drop it, place it in your inventory, or interact with it in any way.
Seems if I hide the bugged board from my cursor I can still interact with things normally and even pick up new objects on my cursor. Not totally sure what the consequences are of this but I can't imagine they are good. I'm betting I could even repeat the process and have a well of bugged boards forever lost to cursor-land
edit: yes, it is repeatable. I can create a queue of items on the cursor but only the most recent item can be dropped. everything else is gone forever
edit2: a log out clears everything from the cursor.