To reproduce:
-add RadDateTimePicker and apply Windows7 theme
-enable calendar footer
-when opening the drop down calendar, the date part in the footer is not displayed correctly

Workaround:
 RadDateTimePickerCalendar calendarBehavior = 
     this.radDateTimePicker1.DateTimePickerElement.GetCurrentBehavior() as RadDateTimePickerCalendar;
 RadCalendar calendar = calendarBehavior.Calendar as RadCalendar;
 calendar.ShowFooter = true;
 calendarBehavior.PopupControl.PopupOpening += PopupControl_PopupOpening;

private void PopupControl_PopupOpening(object sender, CancelEventArgs args)
{
    RadDateTimePickerDropDown popup = sender as RadDateTimePickerDropDown;
    if (popup != null)
    {
        popup.Height = 250;
        popup.Width = 280;
    }
}