It would seem that when you pick up assembly machine or stone furnace which was leveld up by this, it will drop every lover variant.
so an epic one drops one rare, one uncommon and the base item on the ground

Hey thanks for the report,
Sounds like it'll be the mine entity not set correctly in the code, but let me investigate.

Pushed a fix

Just an FYI on the fix for this, it caused me and my friend to be unable to play on our map. We made sure to clean up all the lower varients that had been dropped, but no good. I can play the map solo, my friend can play the map solo, but when either of us hosts and the other attempts to join we get a desync. It's not instant. It happens at different times for different autosaves, but it is consistant on a specific autosave.

Pushed a code change, please let me know if you still experience de-syncs.

This did fix it! Apologies for the delay.