Custom Block Models look strange in U.I.s

Models for custom blocks in add-ons looked rather strange in any U.I.. Back bones show on top of front bones displayed in U.I.s.

Steps to Reproduce:
1. Download the add-on attached
2. Make a world with the behavior and resource packs enabled (turn on Holiday Creator Features, and set it to Creative mode)
3. Run the command "/give @s test:oak_stool"
4. Notice the model in your hotbar looks off to its original image.

Expected Results:
The 3D Block (Oak Stool in this case) in your hotbar should look like the example image called "normal_oak_stool.png"

Observed Results:
The Oak Stool in your hotbar displays bones clipping through each other (as seen in "bugged_oak_stool.png")