Shulker boxes lose their "Lock" tag when mined.

To reproduce:

• /give @a minecraft:red_shulker_box 1 0 {BlockEntityTag:{Lock:"Key"}}

• Place the block
• Right click and observe "Shulker Box is locked!" message
• Mine the block and place it again
• Right click and the Shulker opens.

This makes lockable, moveable inventories impossible in adventure maps.