Advancement background does not find texture from resources.zip embedded in world folder

The bug

The advancement background is not using textures provided by the resources.zip (world) resource pack in the world folder.

How to reproduce

1. Create a new world
2. Place the root.json file in the world data/advancements/custom
3. Place the resources.zip file in the world folder
4. Reopen the world
   → You will see that the advancement uses the modified bedrock texture but is unable to load the background text

Notes

• You can load the resource pack as external one to make sure that advancement backgrounds are working and the used files are correct.
• It looks like it is working correctly the first time you open the world directly after starting the game, but upon reopening the world it is not working anymore.