I'm open to discussion on this behavior, but I think if a group layer is unchecked, then checking a child should not display the child. Currently, even if a parent is unchecked, checking a child will show the child in the map.
To reproduce this behavior:
- Make sure you have at least one theme in your database.
- Uncheck Themes in Map Layers.
- Toggle the check box next to your theme name under the Themes group layer.
Even though Themes is unchecked, placing a check next to the theme name will show the theme.