When wearing certain items in the helmet slot, such as player skulls (haven't tested it with other items, but it's possible the issue is present in other cases as well), the rest of the armour slots graphically glitch, usually in the manner shown in the attached photo. Edit: also causes graphical glitches with in potion/beacon effects GUI when wearing and holding a skull at the same time.

What I expected to happen was...:
Armour slots to appear normally regardless of the item in them.

What actually happened was...:
Sometimes when placing certain items in the head slot, the armour GUI graphically glitches.

Steps to Reproduce:
1. Summon a player skull.
2. Put it on your head.
3. Observe (it doesn't seem to happen all the time, so it might take a few tries).