{BLOCKING LIVE CONTENT] Skeleton & Stray projectiles don't hurt the wither

Release_809752 from 1.2.13

Summary: Regardless of the projectile set, the Stray and Skeletons do not damage the wither with their arrow fire.

Impact: In Monster Battle Arena, Skeletons and Strays are used to battle other mobs, including the Wither. This negativley effects the experience as players will expect skeletons to be able to damage the wither.

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.
2) Load up the world. (or monster battle arena live on the store)
3) Press the button to have the wither and skeleton fight. Alternativley in MBA unlock the wither, summon it and some skeletons on one side and start a match.

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.

Repro Video: https://youtu.be/e8gJyjaOJFs
Monster Battle Arena: https://www.youtube.com/watch?v=AN26HZ31DHY&feature=youtu.be
Attached: Repro World with Included Behavior pack