How To Reproduce:
- Place an object by hand
- the Last User flag will be set
- use the Upgrade Planner to replace the object
- the Last User flag will be gone from the replaced object
This provides the potential for players to grief remotely and anonymously on a multiplayer server that has bots available.
(also related to the Upgrade Planner, this bug - /viewtopic.php?f=35&t=66695&p=407512 - is reproducible in 0.17.7 and adds further griefing potential)