Update: further testing with less-precious materials indicates that any block placed in the chunk disappears when the world is left and re-joined, and any block that is removed from the chunk is replaced upon exit/return. This means breaking the block over and over essentially turns into a duplication glitch.
Update: further testing with less-precious materials indicates that any block placed in the chunk disappears when the world is left and re-joined, and any block that is removed from the chunk is replaced upon exit/return. This means breaking the block over and over essentially turns into a duplication glitch.