Block cracks don't appear on the lower halves of doors when zombies are breaking them

The Bug:

Block cracks don't appear on the lower halves of doors when zombies are breaking them.

Steps to Reproduce:

1. Ensure that the difficulty is set to "hard" and the "mobGriefing" gamerule is set to "true" by using the commands provided below.

   /difficulty hard

   /gamerule mobGriefing true

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

   /summon minecraft:zombie ~ ~ ~ {CanBreakDoors:1b,ArmorItems:[{},{},{},{id:"minecraft:iron_helmet",Count: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, look at the lower half of it.
6. Take note as to whether or not block cracks appear on the lower halves of doors when zombies are breaking them.

Observed Behavior:

Block cracks only appear on the upper halves of doors and not the lower halves.

Expected Behavior:

Block cracks would appear on both halves of doors.