When you place and then disarm a crossbow trap, you’ll always get long string, regardless of what you used to create the crossbow trap. So if you make a crossbow trap with two short strings, you can place and then disarm it to get a four short string profit. It’s not massively game changing, but it does make obtaining thread significantly easier for the character with high enough trapping.
An exploit to be sure, and easy enough to fix by increasing the number of short strings required or removing the option to use long string, but it is more of a limitation of the engine than something operating in a faulty fashion. The game just doesn’t care which recipe was used, so it really can’t track what was used to make it without having multiple identical items with different recipes, and that would cause all manner of horrible clutter. They could try adding on some new variables to items, much as you can have cursed items in more traditional roguelikes, but those are generally dealing with FAR fewer items at any given time… It seems extremely doubtful that anything will be done about this in any sort of practical timeframe, so I recommend enjoying the windfall or using your ill-gotten gains as kindling to ease your conscience. Or build a few cargo carriers, deriving all your rope from rags, you will likely never complain about an abundance of thread again…
I was actually fortunate enough to find wreckage filled to the brim with ruined cargo carriers, but thanks for the suggestion. I AM using this to make steel bolts from wooden bolts though, so that’s advantage enough. Seems like this is done for now!