When the SelectedValue property of the RadDateTimePicker controls is bound to a TimeSpan (10:13) and such time does not exist in the drop down, the SelectedTime property is set to null.

As a workaround, you can subscribe to the DropDownOpened and SelectionChanged events. In the DropDownOpened event handler, you can get the current time using the SelectedTime property. Then in the SelectionChanged event handler, you can set the preserved value to the SelectedTime property of the RadDateTimePicker. 

public partial class MainPage : UserControl
{
	private bool IsLoadedFirstTime = true;
	private TimeSpan? SelectedTime;
	public MainPage()
	{
		InitializeComponent();
		this.DataContext = new MainViewModel();
	}

	private void StartDatePicker_SelectionChanged(object sender, Telerik.Windows.Controls.SelectionChangedEventArgs e)
	{
		var control = sender as RadDateTimePicker;
		if(IsLoadedFirstTime && control.IsDropDownOpen)
		{
			control.SelectedTime = SelectedTime;
			IsLoadedFirstTime = false;
		}          
	}

	private void StartDatePicker_DropDownOpened(object sender, System.Windows.RoutedEventArgs e)
	{
		var control = sender as RadDateTimePicker;
		if(IsLoadedFirstTime )
		{
			SelectedTime = control.SelectedTime as TimeSpan?;
		}
	}
}

Observed when the input mode is TimePicker.

It happens with US culture.

Available in LIB version 2015.3.1019, it will be also available in the 2015 Q3 SP1.

In your documentation you describe how to define custom format in ShortDatePattern and ShortTimePattern. But how can I use a format like CultureInfo.DateTimeFormat.SortableDateTimePattern or CultureInfo.DateTimeFormat.MonthDayPattern? It does not work at me.
The same problem I have, if I want to use long date and short time or short date and long time.

Thanks

when on Month view change year by prev/next button and select same month, year  is not saved

It happens when the control is focused and you press tab in order to focus next control.

Available in the 2014 Q1 Release.

For reference Ticket ID: 766908.

Focus is always the first date (top left corner) from the Calendar when DropDown is opened

The parser swap the date and month part so when you enter 11.3 it is parsed as 3.11.