Advancement backgrounds render translucent pixels as opaque

More loosely relates to these issues: MC-144009 MC-145821 MC-164001 MC-165403

The bug

If textures used for tiling the background of the advancement window are made translucent, they still render completely opaque in-game. This is unlike the outer window and tabs, which correctly render translucent as expected.

How to reproduce

1. Download and apply the attached resource pack
2. Enter the advancements window
3. Observe

Expected results

Translucent background.

Actual results

Opaque background.