MC Ver: 1.12.2
Mod Ver: 1.0.2.45

Over the past two weeks we've been getting reports of a duping bug with the chisel on our servers.
This is one of the reports we've received which contains the steps to reproduce.

Hello!
I’m TvoyMakar/Nogologon. I’m writing about the duping issue.
So here’s the process:
Take diamon chisel -> right click -> put any chisel-related blocks -> shift+right click on any chiseled version of blocks -> close the chisel window -> open chisel window again via clicking right click -> high chance of blocks being there even after taking them out previously

We've tested it and whilst it's not an 100% chance to dupe it's certainly reproduceable in a manor that can be heavily abused.
It may be beneficial to have a config setting if possible to disable the inventory of chisels holding items outside of use, so instead when closed, if the input slot still contains items- they drop instead.

Forgot to add tags, my bad.