Michel,
That was my assumption as well. So how do you reconcile the guidance in the Group dialog for mutex buttons that says:
"It is highly recommended that button groupings are migrated through Scenes by adjusting respective On Levels. By doing so correct status of the buttons are also reflected in ISY regardless of their groupings"
In my scenes, the secondary buttons don't show up as something that can be adjusted. Is the disconnect for me because my switches don't support this of setting On Levels feature so that is why they don't show up in the scene as a device that I can affect the LED levels with?