When moving items from hoppers into other hoppers/containers, the item will sometimes be duplicated. Tested with a variety of items, and got the duplication with all. Seems most frequent with redstone. Not tested in survival.
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This was a bug with the last snapshot. I think it was fixed. I will try to reproduce though for funnies. 😛
Duplicate of: MC-5998 - Please use the search function to see if your bug has already been submitted.
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