Armored mobs spawned from spawners doesn't drop thier armour or/and itemfrom their hand

Put the summary of the bug you're having here

What I expected to happen was...:

Zombies from spawner to dropp their armour and held items, Skeletons spawned from spawner also to dropp their armour ** 

What actually happened was...:
Zombies and skeletons  from spawners ** doesn't dropp their armour or held items not even whit looting 3, but armoured mobs spawned in the wild does drop their armour pieces sometimes. 

Steps to Reproduce:
1. Wait for mobs to spawn whit armour from spawners (zombie spawner, skeleton spawner or trail chamber spawner) 
2. Killing armoured mobs
3. Mobs doesn't drop their armour