Cannot set weapon slot of a mob/armor stand with armour or player/mob head (/replaceitem)

The bug

When using /replaceitem you can not set any type of armour or mob heads to slot.weapon.

How to reproduce

1. /summon armor_stand
2. /replaceitem entity @e[type=armor_stand,limit=1] weapon minecraft:iron_chestplate
3. Error: "Could not put [Iron Chestplate] in slot 98"

Note that other items, such as stone blocks, work.