1. Start Creator with dark theme.
2. Open a project.
3. Go to Projects mode.
   You'll see dark controls on a brighter background:
   
4. Go to "Tools" -> "Options..." -> "Environment" -> "Theme".
5. Select the default theme and click "OK".
   Some controls become bright, others stay dark:
   
6. Close the project.
7. Open the same project again.
8. Go to Projects mode.
   Now all controls use the default theme:
   

Changing the theme should either update all controls at once or it should change nothing at all until Creator is being restarted.