Perhaps I am not referring to the correct part of the control... in the Timeline view, above the ticks and below the bar containing the datetime picker and the view selection buttons, there is a gray bar containing the date which stretches across the visible calendar. If my Timeline view is 1 day but I set the visible hours to be - for example - 06:00 to 20:00, that gray bar resizes itself and no longer stretches across the visible calendar. It isn't the same as the scroll bar at the bottom of the control. Here's some simple xaml to display the behaviour:
Jonathan