Operating System: All
The selected ribbon task button (e.g. "Home") can be deselected by selecting it
a second time.
After looking at the code in CommandToggleButtonGroup, I suggest either
enhancing the class or creating two different group implementations: One that
allows the selection to be cleared (current) and one that don't.
CommandToggleButtonGroup should be enhanced to support the mode that disallows
unselecting the currently selected button and clearing the selection.
Moving to 5.0dev branch for fix.
This should be fixed in the latest 5.0dev drop.