I think that you are missing the ElementName in the ItemsSource Binding. In this case the ElementName is the x:Name of your window or UserControl. IsSynchronizedWithCurrentItem="True" TabIndex="10" Grid.Column="1" Grid.ColumnSpan="4" ItemsSource="{Binding Path=ParameterNameCollection, ElementName=UserControl, Mode=Default}" SelectedValue="{Binding SelectedParameter.Name}" Style="{DynamicResource BaseComboBox}">