When the MinTimeRulerExtent of a view definition is lowered (to the point that the view does not have a scrollbar) and the EnableSmallAppointmentRendering is true, the content of the group headers is not displayed. 

Disscused here: http://www.telerik.com/forums/freezing-row-in-timeline-view-in-radscheduleview

Make it possible to set a range of dates in which the RadScheduleView can navigate its ViewDefinitions. Navigation in that range should be possible via the left/right buttons in the top right corner or the DatePicker control also at that location.

Ability to distinguish beween types of group headers and apply fixed width to one type of group headers and force the rest of them to calculate their size automatically.