This happens only with editable ComboBox in Silverlight.
When the ItemsSource for a RadComboBox is bound to a collection with two different properties, id and ID. When I bind SelectedValuePath to one of the properties, changing selection throw error: "Ambiguous match found" exception.
When moving through elements(checkbox+ text) in RadCombobox with the keyboard, focus of combobox is not changed as expected. Sample project attached.