This is true for the DbSelectedDate
property of RadDatePicker and RadDateTimePicker as well as for the SelectedValue
property of RadComboBox. The reason for that is these properties are of nullable type (accept null values). Note that the same is true for the SelectedValue property of the regular MS DropDownList.
Still settings values for these attributes should work as expected and they will be 'recognized' at runtime.
the Telerik team