The tail will not render when viewed in spectator mode, or when the entity is on the same team as the player.
Steps to Reproduce:
Spawn a tadpole
Make it invisible:
/effect give @e minecraft:invisibility infinite
Change gamemode to spectator
Observed Behavior:
The tail of the tadpole will not be visible when looking at the left-hand side of the entity:
[media]
Expected Result:
The tail would be visible at all times, regardless of the entity's effects, or the gamemode the player is in:
[media]
Possible Fix:
Add a 'backside' to the texture of the texture of the tadpole's tail. Here is a resource pack which demonstrates this fix (could cause z-fighting):
[media]
Can confirm. As stated in the issue, this only occurs when viewing the tadpole on the left side.