The pickers for the custom fonts for Message List styles do not offer Bold or any other non-italic non-oblique non-standard style. (I am going to attach a screenshot if possible to show what I’m referring to)

Reproducible: Always

Steps to Reproduce:
1. Open "Configure Kmail…", tab Appearance
2. Tick "Use custom fonts"
3. select "Message List - Unread Messages"

Actual Results:  
The "Font style" list only shows "Normal", "Italic", "Oblique", but not "Bold" or any other styles.

Expected Results:  
The "Font style" list should also offer "Bold" and possibly other styles.

My (uneducated) guess is that this is related to the disabling of the "Font" list.

The "Font" list is grayed out and stuck at "Monospace". When switching for example to the "Message List" custom font, I can select other fonts. Selecting Monospace will also only offer Italic and Oblique, while several other fonts (including the font I am ultimately using for the Message List) also offer Bold etc..

This is with kmail from debian experimental: Version 5.2.1

Using:
KDE Frameworks 5.22.0
Qt 5.5.1 (built against 5.5.1)
The xcb windowing system