Damage to Mob - Animated Hearts Inconsistent

Hearts of damage suffered animation only shows when mob struck by sword or axe.

What I expected to happen was...:
Hearts lost to animate when mob suffers any damage. eg. Fists, Falling, or Fire.

What actually happened was...:
Animation, particles only show if sword or axe equiped and used to strike mob..

Steps to Reproduce:
1. Equip with sword/or axe.
2. Strike mob for damage - watch "hearts lost" animation.
3. Switch to another object, or empty hand.
4. Strike with empty hand or object- note lack of animated "hearts lost"
5. Watch zombie burn in daylight - note lack of animated "hearts lost".
6. Observe mob fall from sufficient height - note lack of animated "hearts lost".