Overloading a chunk with data will cause it to revert to its old state

The bug

When too much data is stored in a chunk, Minecraft will refuse to save the chunk. When a chunk is in this state, anything in it can be removed and taken out of the chunk and when that chunk is unloaded and reloaded, it will be revert to the state it was before. To overload a chunk with data, the perfect item to use are written books, you can store massive amount of data in them. These books are filled with heavily randomized unicodes to stop Minecraft's compression algorithm.
If you are interested what the actual content is in the books, you can check it out here. This also works on multiplayer by using nether portals to save the chunks easily.

How to reproduce

1. Download this world.
2. Extract the world in .minecraft\saves.
3. Enter the world and look around the beautiful spawn.
4. Enable chunk borders by pressing F3 + G.
5. You'll see a lever on a diamond block, switch it so the redstone lamp goes off, so the items out of chest B go into chest C.
   → At this moment, the chunk is overloaded with data and you are free to edit anything, upon unloading and reloading the world, everything will be reverted to its old state
6. Locate the chests inside of the chunk border, they are filled with some spicy items.
7. Pick them out and move them over to the other side of the chunk, those chests are one block outside the chunk, just put the items in there (instructions are also in the signs).
8. Reload the world.
   → You just duplicated everything that you put into the chests outside of the chunk