The bug is when you hold custom heads or any type of head in the 9th hot bar slot the offhand shield icon becomes scribbled and the armour slots turn black when you wear it. When you hold the skulls / heads in 1st person view mode I think it appears to look a bit bigger.

What happened was...:
In the 9th hot bar slot in inventory shield icon in offhand turned black and when equiped all other armour slots turn black

Steps to Reproduce:
1. Hold any type of head in 9th hot bar slot. You need to hold it in 9th hot bar slot.

2. Open your inventory. Notice that the shield icon in dual hand slot turns black.

3. When you equip head notice that other armour slots turn completely black.