The bug

Heads and skulls on a wall cause z-fighting when viewed in Spectator mode or at certain angles. This is not the case for Dragon Heads.

The bug is caused by the fix of MC-183915.

How to reproduce

1. Place a head or skull on a wall.
2. If a wall head is placed, switch to Spectator mode to view it from the inside.
   → The head shows z-fighting from the side.
3. If a wall skull is placed, view it from below.
   → The skull shows z-fighting from the side.