Hi Jerry, I'm afraid I am unsure on how to keep the block's NBT data when it's placed in the world. I'm not sure if that is possible. Thus, the block is reverted to its uncompressed form (you lose 8 blocks).
I didn't want the users to lose their items so I just prevented to compressed blocks from being placed.
I'll look into storing where the blocks are placed in the world and checking if that block is broken --> drop the compressed block instead of the uncompressed item.