Summary:
When the HUD opacity is adjusted, enchanted mob heads and shields are unaffected.

Steps to Reproduce:

1. Obtain a mob head and shield
2. Enchant both items
3. Put both items in the hotbar
4. Go to Settings > Video and lower the HUD opacity to 1%
5. Exit the settings and wait for the hotbar to disappear

Observed Results:
The mob head and shield are unaffected by the HUD opacity.

Expected Results:
The mob head and shield should be affected by the HUD opacity.