RadCalendar selection works on a Toggle
principle. This means that if you click a cell the selection is toggled - selected or unselected. For example:
When a date is unselected then the SelectedDates collection of RadCalendar is empty and by default the new DateTime(1980, 1, 1); value is returned. This is an expected behavior with the current design of the control. However we will re-consider this behavior one more time for the upcoming major release. Thank you for your feedback.
the Telerik team