mobs not taking fall damage

if i summon mobs from the build height, some mobs, mostly the undead ones,  don't take fall damage if they land on buttons or hoppers. 

 

Steps to reproduce: 
place down a hopper, button, lever, or slab.

Summon a mob (zombie or skeleton) at a height that they will die from fall damage.

 

expected result- mob will take fall damage and die.

 

platform: Bluestacks on windows 10