If you repeatedly right click an item very fast, it sometimes duplicates, haven't got it to work in survival, only creative.
MC-7202
Inventory Item Duplication
Resolved
Duplicate
0
user-4968d
(Unassigned)
Unconfirmed
Snapshot 13w02b
Retrieved
Duplicate of MC-341, please use the search function to see if your bug has already been submitted. Currently over 42% of tickets are being closed as duplicate.