Original report:

Hi, I think I've encountered a bug so I'm going to describe it here to see if it's a bug, as I suspect or it's an already known one, and to put it on record for it to be fixed at some point.
The thing is: I had lemon jam and I was crafting myself a sandwich, after opening the 5 jars I used, it resulted into two different stacks a 4 units stack and a single unit stack, as they where from different batches and they had different expiry dates. In order to make myself a single batch of sandwiches I decided to put all the jam jars together into the crafting table so I would obtain a single stack of 5 units. The bug comes into the fact that, after doing it, there where 5 empty jars into the crafting slots and 5 jam jars in my inventory, a total of 10 jars thus the items had been duplicated.
I'm in version 1.20.1, and I have the following mods: TerraFirmaCraft, Patchouli, JEI and Jade, and no addons. And I've tried following this steps on a creative world and I can replicate it consistently and duplicate the ammount of total jars.
PS: If something is not clear or you need more info, I'll be able to provide it.