Mobs wearing Helmets do not burn during the day

I was playing around on a flatlands world I spawned about 200 zombies about 10 of them wore armor and when the daylight appeared the zombies that did not have armor burned but the 10 that did have armor, did not burn. Within the attachments I will show photos of this accruing (note the villager zombies and any zombies with items in there hands burned just as fine).