public class CustomRadComboBox : RadComboBox
{
	protected override void OnTextChanged(string oldValue, string newValue)
	{
		if (string.IsNullOrEmpty(newValue))
		{
			newValue = string.Empty;
			Dispatcher.BeginInvoke(new Action(() =>
			{
					SelectedItems.Clear();
			}));
		}
		base.OnTextChanged(oldValue, newValue);
	}
}