It's possible to duplicate items using this plugin.

Example:

Have 1 pre-made sign in your inventory. Place the materials to make a sign in a crafting bench. Now put the pre-made sign on top of the sign that is currently shown as the outcome of the bench. They will stack, you can grab them off the bench now, and the items originally used to craft the first sign will not be taken. Thus, you get a free sign. Have only tested with signs, I'd assume it works with any item.

Should be fixed as it can no longer affect Result slots.

I'll test this later tonight or tomorrow, thanks haveric.

I'm going to work on some more bugs/features so if you need a jar, let me know. Otherwise you can build it yourself for now. I'm not going to release an official jar just yet.

Tested, seems to fix the issue. Thanks for the ultra quick fix haveric.

I'm getting build errors (my bukkit/vault/cb are a bit out of date which is probably the issue), I can wait for an official jar if needed, though if you have time a jar would be awesome.

I added a test folder under versions with the fix.