Removing "undead" from undead mobs doesn't allow them to damage wither.

Release_809752 from 1.2.13

Summary: Strays, skeletons and wither skeletons are unable to damage the wither even when removing the family "undead" from them.

Impact: In Monster Battle Arena, Skeletons and Strays are used to battle other mobs, including the Wither. This negatively effects the experience as players will expect skeletons to be able to damage the wither when they're shooting at them.

Repro Steps:
1) Edit skeleton behavior to be able to target the Wither. I have attached a world with included resource pack that will reproduce this and remove "undead" from their family.
2) Load up the world.
3) Press the button to have the wither and skeleton fight.

Observed Results: The arrows fly through the wither and don't damage it at all. However an enderman modified to shoot arrows will damage the wither.

Expected Results: The skeletons should be able to shoot the wither and damage it. Further to MCM-200, the devs said "undead mobs are said that they can't hurt the wither." So removing undead family from the mob should result in it being able to damage the wither.

Repro Video: https://youtu.be/e8gJyjaOJFs
Attached: Repro World with Included Behavior pack