Summoning ArmorStands with custom equipment doesn't render the equipment

When attempting to spawn ArmorStands with custom equipment using /summon, or adding ArmorStand equipment via /entitydata I was expecting the equipment to render. Instead, the ArmorStand rendered as if it had no equipment on.

How to reporduce:

1. create a new world
2. type
/summon ArmorStand ~ ~1 ~ {Equipment:[{},{},{},{},{id:"minecraft:diamond_helmet"}]}

OR, type
{{/summon ArmorStand ~ ~1 ~ }}

followed by

/entitydata @e[type=ArmorStand] {Equipment:[{},{},{},{},{id:"minecraft:diamond_helmet"}]}

in either case, the equipment will not render.

Note that this issue is the same as MC-86438, however the issue was dismissed as invalid when the reporter's ticket was found incomplete.