Individual theme settings not visible

Ways to reproduce:
1. Installing Drupal from scratch (go through database setup etc.).
2. Fire up /admin/build/themes/settings and notice that you can't select Garland settings (which is the default theme), only generic theme settings are visible. See attached screenshot.

Expected behaviour:
Specific Garland settings should be visible, because it is definitely enabled since I'm using it. :-P

Temporary fix:
This can be fixed by going to the theme listing at /admin/build/themes and enabling Garland.

Sketch of permanent fix:
One way of fixing this issue is to ensure that the default theme always is enabled.

Notes:
This bug has shown up for me in other contexts than a new fresh install. However, I have not been able to reproduce it. A little more tweaking might do it.

Also, is the idea to hide specific theme settings when only using one theme? It is not an optimal solution. Maybe this is a bigger design issue?