It seems the latest version of FastWorkbench for 1.19 introduced a little dupe bug,

Steps to replicate:
Right click to craft with only enough items to craft 1 of the item.
It should then craft a stack of the item despite not having enough resources to do so.
This works in either the crafting inventory or the fastworkbench modified vanilla workbench.

it has been isolated to be an interaction with crafting tweaks, a fix is in the works

Thanks, much appreciated!

It's reproducible using Valhelsia 5, v5.0.18, as an extra data point (and was not present in 5.0.17). I don't have time to pinpoint it to a specific mod interaction right now (nor will I for the foreseeable future due to surgery in the morning), so this isn't the most useful information other than that it may help as a starting point if there's anybody else reading this that has time to help narrow it down from there.

This bug can also cause item loss if you have more than enough to craft a stack.

Cannot reproduce in isolation in singleplayer or on a dedicated server.