Putting any stackable item in a specific slot in the inventory and then pressing shift + left button duplicates the item, watch the video: https://www.youtube.com/watch?v=xgoK69hjue8

Apparently, this bug can be done in any furnace of the mod.

Version: 1.19.1

Thanks for reporting this bug, I will fix it soon

Fixed in 1.19.2-1.0.1, 1.16.5 and 1.18.2 soon