When repairing two unenchanted pieces or tools/armor (from what I can tell anything that can break) it will produce the tool you wanted, but doesn't clear the crafting recipe.
MC-47178
Armor duplication glitch
Resolved
Duplicate
0
Duplicate of MC-46715 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.