Previous/Next Page buttons render translucent pixels as opaque

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

The bug

If the buttons used for going to the previous or next pages in a book are given a translucent texture, they will render as completely opaque.

How to reproduce

1. Download and apply the attached resource pack
2. Open a book and quill
3. Optionally, go through pages

Expected results

The buttons would have visible text.

Actual results

They look like solid rectangles.

How to fix

Permit translucency for these textures in this context.