When you combine it in any other crafting grid, it's fine. It's just an issue with the SophisticatedBackpacks crafting grid upgrade. And it's only a problem with redstone dust with a pen. If you combine 2 pens, it works as intended. I made this issue report on their page as well.

The other dev in the sister issue reported how to fix the issue:

This needs to be fixed by Redstone Pen mod - in their ExtendedShapelessRecipe::getRemainingItems method they clear the passed in crafting grid which I only pass a copy of to the recipes so they are not actually clearing the grid shown to the player but as a result the logic that is there to actually take care of spending the ingredients gets back empty crafting grid that has height and width of 0 and thus it uses ingredients in 0 slots. getRemainingItems isn't supposed to make any changes to the crafting grid and so that needs to be fixed on their side.

Yeah, sorry for not including all the info in both. it's just I was writing both reports up at the same time so that I can quickly link the 2 reports together. I was in a rush and their github asked for formatting and this one didn't so I was hoping the sibling-issue would have been enough to cover anything that you were missing.

Hey Ynaught, ty for the hint. It seems we have to dig a bit deeper here. Can you provide the versions of Minecraft and the two mods? It would help tracking the problem? --> Edit, just saw the versions in the sibling-issue.

Ty for forwarding, I'll schedule and try to get a fix that works universally. P3pp3r has already done a great pre-checking.

Hey Ynaught, I have bad news - came to the decision to discontinue modding due to time constraints.

I took a quick look into the code for resolving this before archiving the repository, but I could not find a proper solution without the risk of breaking something else. Technically P3pp3r does everything proper and correctly when handling the crafting grid. In the past, the stuff in the crafting grid was changed in-place, allowing to modify item data e.g. to make repairs or fill the redstone pen. Now a result is returned instead, but only the items, which does not allow repairing anymore. Fortunately, MC and most mods still pass the crafting grid as reference - so the old method still works. In SBP, the new return-copy methods is applied (absolute correctly). To resolve this compat issue, I would have to implement mixins (hook into the MC crafting function globally), which is prone to error and mod compatibility on other sides.

Sorry about leaving it there. Cheers,-