I was attempting to dispense mob heads onto villagers and zombies today, and the dispenser would either misfire or shoot out the item as a drop. I tried with multiple zomibes, including those spawned holding items and wearing armor (which should therefore be the "type" of zombie that can hold and wear things), and it wouldn't work with anything, including helmets, which armor wearing types of zombies should be able to wear. Villagers won't wear mob heads either.

To recreate bug:

Place a dispenser next to a villager or zombie, put a mob head or helmet in it, and fire it.

Expected behavior:

the villager or zombie will be wearing the item

Actual result:

The dispenser misfires or throws the item on the ground.

Additional note: with further testing, I have been unable to get zombies to pick up equipment or weapons from the ground either.