Mob cross arms (bow position) when targeting and holding something in the offhand

Whenever a type of zombie (except for drowned) has an item in it's offhand, it correctly positions like a player, but when it is chasing/attacking an entity, it crosses its arms as if it is charging a bow.

How to reproduce:

1. Spawn a zombie.
2. Type command: /replaceitem entity @e [type=zombie] slot.weapon.offhand 0 shield
3. Go into survival mode or spawn a villager.
4. Notice the position of the zombie’s arms when it is chasing/attacking.

Has been reported to affect zombie, husk, pillager, vindicator or evoker at least.