As you can see here http://gyazo.com/f4d4ef390c42c038949ea7cdd2bb3934 you can see a bunch of redstone which was dupelicated via http://gyazo.com/f16ac352707a97574fd6df3135d065f2
MC-56844
Dupelication Glitch (Chunk Glitch)
Resolved
Duplicate
0
Joshua Lee
(Unassigned)
Unconfirmed
Minecraft 14w21b
Retrieved
Is this the bug you're talking about: MC-51610