Scroller in Realms screen renders translucent pixels as opaque, unlike elsewhere

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

The bug

If scroller.png is given a translucent texture, it will correctly render as translucent in most contexts. However, in some realms menus, it renders completely opaque, which is notably inconsistent.

How to reproduce

1. Download and apply the attached resource pack
2. Navigate through menus that have a scroll bar
3. Go to Realms

Expected results

All places that use the scroller would render it as translucent.

Actual results

Most do, but this screen has it as opaque for some reason.