The bug

When a zombie starts breaking a door and during this the door gets replaced the zombie continues breaking this block.

_{Additional description by kingsupernova:}
If a zombie begins to break a door but the door is removed before it's done, it will continue to try to break the block in that space. The door breaking sounds will continue to play even if there isn't a block there anymore, and the door particles will appear when the door would have broken. If the door is replaced with another block, that block will be broken instead, no matter what it is.

Expected behavior

Zombies and vindicators should not continue to break doors once a change in blocks has been made.

Reproduction steps

1. Ensure that the difficulty is set to "hard" and the "mobGriefing" gamerule is set to "true".

   /difficulty hard
   /gamerule mobGriefing true
   

2. Build the setup as shown in the attachment below: setup.png
3. Whilst standing on top of the diamond block, summon a zombie that is able to break down doors.

   /summon minecraft:zombie ~ ~ ~ {CanBreakDoors:1b}
   

4. Stand on the opposite side of the door as the zombie, switch into Survival mode, and get it to notice you.
5. Once it begins breaking the door, switch into Creative mode, destroy the door, and watch the behavior of the zombie closely.
   The zombie continues 'breaking' the non-existent door

How to reproduce (outdated)

See Minecraft - Block Breaker

Additionally:

• Set the difficulty to "hard"
• Spawn the zombie or vindicator with {CanBreakDoors:1b}

Note: The meta data of the placed block should not have bit 2 (2²) set, otherwise the zombie will recognize it as open door.