Elder guardian has z-fighting on the inside

When viewed from the inside, the elder guardian's texture has z-fighting

What I expected to happen was...:

no z-fighting, texture is darker everywhere

What actually happened was...:
there is 2 pixel wide z-fighting of a brighter texture vs darker texture

Steps to Reproduce:
1. Summon and elder guardian with no AI 

/summon minecraft:elder_guardian ~ ~ ~ {NoAI:1}

2. put it in water so the spikes extend and the z-fighting is more visible (optional)

3. switch to spectator mode

4. fly inside the elder guardian

5. notice the z-figting on the top  texture  towards the front of the elder guardian