gamerule fallDamage false doesn't turn off fall damage for mobs

The bug

If the gamerule fallDamage is false, mobs can still take damage from falling.

How to reproduce

1. Do /gamerule fallDamage flase
2. Take a mob that is affected by fall damage and leash it
3. Fly high enough and then fly back to the ground

Notice how a mob can still get hurt from a fall