Separate Fill Alpha does not work on font outlines when outline size is set to 1

Font outlines render underneath the text, meaning that partially transparent text will allow the outline color to show through. This can be avoided by enabling Separate Fill Alpha. However, that option doesn't work when outline size is set to 1.

1. Create a text block widget with a font outline
2. Set opacity to 0.5
3. Check "Separate Fill Alpha"
4. Set Outline Size to 2
5. Note that text appears partially transparent
6. Change Outline Size to 1
7. Text now appears darker