The video includes the full reproduction steps. The image shows a screenshot of the unexpected behavior when moving inside the Happy Ghast.
Steps To Reproduce:
Create a new Creative world with default settings.
Obtain a Happy Ghast Harness from the Creative inventory.
Summon an adult Happy Ghast using the command `/summon happy_ghast ~ ~ ~`.
Equip the Happy Ghast with the harness by right-clicking on it while holding the harness.
Use the command `/data merge entity @e[type=happy_ghast,limit=1] {Age:-24000}` to set the Happy Ghast's age to -24000.
Observe that the harness layer disappears from the outside view of the Happy Ghast.
Enter the interior of the Baby Happy Ghast by moving inside of the Happy Ghast to see the harness layer rendered incorrectly inside.
Observed Behavior
The harness layer that is visible on the adult Happy Ghast disappears entirely from the external view, making it appear as if the harness is not equipped. Upon inspecting the Baby Happy Ghast from the inside, it becomes evident that the harness layer is still rendered; however, it is not scaled correctly.
Expected Behavior
When an adult Happy Ghast is equipped with a harness and its age is set to -24000, the expected behavior is that the harness layer should remain visible and properly scaled when viewed from outside the Baby Happy Ghast. The harness should adapt to the size of the Baby Happy Ghast, maintaining its intended appearance and functionality. Specifically, the harness should not disappear and should be rendered correctly, allowing players to see the harness layer as they would expect based on the model's design.
Thank you for your report!
We're actually already tracking this issue at MC-300894, so I will resolve and link this ticket as a duplicate.
I suggest also to browse through the main issue for potential fixes.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
Quick Links:
📓 Issue Guidelines – 💬 Mojang Support – 📧 Suggestions – 📖 Minecraft Wiki