Help!!!

When killing any type,the corpses don't get knockback die-it just stays exactly where you killed it,even it is was killed floating in the air.

What I expected happened was..
Mob die like take knockback..

What actually happened was...
Mob die like floating in the air..

Step to reproduce in survival:
1.find any type of mob..
2.and kill one of them
3.and you will see,way mob die like killed floating in the air..

Step to reproduce in creative:
1:spawn any mob by use command summon or spawn egg
2.and kill a mob
3.and they will die like floating in the air.