Incorrect armour textures when switching

What I expected to happen was...:

When switching between armour sets, the newly equipped item should show on my character

What actually happened was...:

When switching from leather to diamond, the colour appeared to be iron but with strips of leather as well. Happens to all armour types. Appears to also happen to armour stands.

Steps to Reproduce:

1. Equip any type of armour.
2. Switch to a different type of armour.

Issue doesn't resolve until you leave the world and re-enter.