When in spectator mode and also in 3rd person view, entities render behind the player's head.

When a player is in the gamemode "spectator", and the player presses F5 (or their keybinds for toggleing perspectives) to enter 3rd person viewing mode, entities render behind the players head, therefore giving such an effect as that part of the entity is invisible. Also noted is that the player's head also renders in fron of glass but not in front of other blocks.