In a LAN world I looked outside of my house at a mountain that was behind a wall of my house and a large area of chunks from the mountain would change into the same group of blocks. They would also change when you look or move around. I went to the mountain and you can see the outlines of the blocks but the blocks aren't right. Placing or breaking a block shows the chunk temporarily, but then it reverts back to the groups of blocks.

To Replicate:

I think that you have to stand behind a wall to block the view to some chunks then after a while look behind the wall at the chunks.