I found a bug with the crafting table. Every time you put in an item in the crafting slot and back out it gives you a furnace backpack. I tried it out in the survival crafting GUI and it works correctly. Im using version 1.14.4.
heres a video that i made showing the bug:
https://youtu.be/PF8KoyQzwS4
Please can you fix this bug as it is a big problem. thanks,

I couldn't reproduce this on 1.14.4 with the latest plugin version. Maybe try updating? I'll reopen if more info becomes available.

I have this bug running vanilla paper 1.15.2 + backpacks remastered + timber plugin ( https://www.curseforge.com/minecraft/bukkit-plugins/timber-plugin ). Every time something has occupied the crafted slot and we remove the item from the slot, a furnace backpack pops up. The video tyepavitt posted shows it like we experience it.

Ok, I'll look into it.

Ok, thank you. Let me know if I can do anything to help you.

Tested with paper 1.5.2 (239), backpacks 2020.0.4, and timber 1.0.7.
https://i.imgur.com/rWA7QRu.mp4

Still cannot reproduce. Are you using the latest versions?

I updated my version of paper (61 commits behind) and Backpacks (from 2020.0.3 to 2020.0.4), timber was on the latest version. Still had issues. I remembered I had edited the config.yml-file in the BackpacksRemastered directory, so I copied that out and let the .jar file create it from scratch again, now it worked fine without creating the furnace backpack. Would you like the edited config.yml file to see if you can reproduce it on your end?

I had edited it so that only the small and large backpack plus the backpack key was available for the users on the server. I realise now that that probably was the wrong way of doing it. What should I do to only let select backpacks be available for crafting?

Yea, give me your modified config. Also, while doing stuff this way shouldn't cause this error, if you want to properly restrict backpacks, you should use the permissions. If you don't have a permission manager, you can just change the "default: true" line under the particular recipe permission to false in the plugin.yml (just open the jar as a zip with 7zip).

This will be helpful as I may add a way of obtaining some backpacks through strongholds, treasure chests, etc. That will be dependent on the permissions of the players looting the chest.

Here it is. Thanks. I had tried to do it that way earlier, but I must have messed something up. I will test that again. :-)

config.zip

Can confirm that this was indeed the issue. Removing these entries from the config causes the described issue in spigot/craftbukkit/paper 1.15.2 regardless of other plugins installed.

I was already planning big changes to the recipe system so whenever I implement these, it will fix the problem. I will leave this issue open until then. Fixes should be in v2020.0.5. Until then, using the appropriate permissions to regulate backpacks solves the issues.