The Bug:

The command block GUI remains open when the said command block is destroyed.

Steps to Reproduce:

1. Enter a singleplayer world and open it to LAN.
2. Place down a command block and open it.
3. Get another player to join the world and destroy the command block.
4. Take note as to whether or not the command block GUI remains open when the said command block is destroyed.

Observed Behavior:

The command block GUI remains open.

Expected Behavior:

The command block GUI would close if the said command block is destroyed.