When shift clicking an item into the grindstone and exiting at almost the same time, the item will dupe.

Dupe bug confirm on Future MC 0.1.8b.

I try with an enchanted diamond pickaxe, I place in the grindstone end I quid instantly the interface, I get back the pickaxe into my inventory and when I reopen my inventory, I saw a new identical pickaxe drop on the floor!!

I can reproduce that indefinitely without any issue, this is a 100% chance of dupe...

I'll take a look at it.

Fixed in 0.1.9