Giants were given the ability to visibly wear armor a while back. Since then, we have been given the ability to do more with equipment slots. Mobs such as Skeletons, Zombies, and even Villagers have been given the ability to wear armor and more. However Giants, Zombie's counterpart, still only function with default armor. This seems inconsistent.

What I expected to happen was...:
Giant to display a block on its head, or a full banner to scale with itself.

What actually happened was...:
I am presented with the message "Could not replace slot 103 with 1 * [Stone]" when testing with Stone, and similarly for other materials.

Steps to Reproduce:
1. Use this command to summon a Giant: /summon Giant ~ ~ ~
2. Use this command when standing within 20 blocks of the Giant to attempt placing a Stone block on its head:
/replaceitem entity @e[type=Giant,r=20] slot.armor.head minecraft:stone 1 0
3. You will be presented with the above message.

Additional Information:
Command for placing a Diamond Helmet on a nearby Giant's head:
/replaceitem entity @e[type=Giant,r=20] slot.armor.head minecraft:diamond_helmet 1 0
Command to attempt putting a Banner on a nearby Giant's head:
_/replaceitem entity @e[type=Giant,r=20] slot.armor.head minecraft:banner 1 0 {BlockEntityTag:{Base:1,Patterns:[0:

]}}_