This bug can duplicate items, like sword,bow,pickaxe,axe,etc.
You need this:
2 Items and nothing else.
How to do it:
Place the 2 items in a crafting table and click shift and the item.
Boooom Your inventory is full of this item.
This is tested in the version 14w05b.
Environment
Operating System: Windows 7 and Ubuntu 13.10 in dual boot. (64 Bits)
Java Version: Update 45 64 Bits and Java SE Development Kit
Blah Blah Blah
Please do not mark unreleased versions (anything starting with "Future Version") as affected. You don't have access to them yet.
Also a duplicate of MC-46715