Transparent texture parts of invisible entities are rendered black when looking at them in spectator mode

The bug

When looking at an invisible entity (or player) while in spectator mode, all transparent texture parts of that entity are rendered black.

To reproduce

1. Spawn an entity with transparent texture parts, such as a villager, a persian cat, or a player with a skin that has transparent texture parts in its outer layer
2. Make that entity / player invisible
3. Switch into spectator mode
   → The transparent texture parts of that entity are rendered black

Video

Minecraft 19w42a 2019-10-20 15-02-11_Trim.mp4