The bug

If any pixels in the pack.png supplied with a resource pack are fully transparent, they will be rendered as fully transparent in-game.

The ticket MC-268929 was swiftly closed as a feature request, in stark contrast to all of the tickets marked as related to it (the only thing remotely close is an older WAI ticket). Given that many of the other tickets related to it have either been fixed so far or are triaged, this may imply that having transparent pixels in pack.png in the first place is not intended design, in contrast to other UI elements.

How to reproduce

1. Download the attached resource pack and place it in the correct directory
2. Navigate to the resource packs menu

Expected results

All transparent pixels in pack.png would be rendered opaque.

Actual results

They are rendered transparent.