In 15w34d, chunks which are empty, yet loaded seem to duplicate one-another if blocks are placed in them.

Steps to reproduce:

• Create a new world
• Enter the End
• Place blocks starting from the main island outwards until the blocks stop appearing solid and appear as just hitboxes or "ghost blocks".
• Press F3 and A
• You'll notice the empty loaded chunks duplicate this new chunk with the ghost blocks. What's even stranger is that these duplicated chunks have solid blocks, so it's not just a rendering glitch.
• Place blocks in a neighbouring chunk and F3 A again, same thing happens.
• Relog while in that empty chunk with the ghost blocks
• You won't be able to move until you are in back on the main island with pregenerated chunks.

This also happens when you create a void world of just air. Since there are no blocks in any chunks, you will be stuck until a block is placed and you relog. Then once you place blocks outside that chunk, and do F3 and A (or chunks are rendered on their own), you'll get the duplicates again.

Attached are some screenshots courtesy of myself and LapisDemon.

I have also attached a crash report. I am unsure if this is related to the problem, but it happened while trying to recreate the above issue. I created a flat world of carpet and broke the carpet to try and get empty chunks. I got the same ghost blocks appearing but this time my game froze and crashed when I came across a generated village.

I have been informed that this does not occur in the A, B or C snapshots of this week (15w34)

Hopefully this helps!