I'd been testing the /recipe command for an enchantment table and I found this exploit.
When in a Worldguard area you're not allowed to open containers in, using the /recipe command doesn't work.
However, doing it twice (or once in certain cases) drops some of the items used to craft the item you were doing recipe for, and places a duplicate of the items dropped in your inventory gui's crafting table.

For enchantment tables, it seems to drop a diamond and a book, so that's two diamonds by using /recipe Enchantment_Table in a protected area twice. I tried it with a beacon and it seems to only drop the glass, but it seems to be a different drop(s) for each recipe, and it stays the same each time you try it.

Can you reproduce this with only essentials installed?

No because it only happens when in a worldguard area you're not allowed to open containers in.

Can you be a bit more specific as to which WorldGuard flag you are referring to?