WPF

<ControlTemplate TargetType="{x:Type GroupItem}" x:Key="SceneGroupItemTemplate" >
    <Expander IsExpanded="True"  >
        <Expander.Header >
            <Border Background="LightSteelBlue" 
                    BorderBrush="SteelBlue" 
                    BorderThickness="1" 
                    HorizontalAlignment="Stretch">
                <TextBlock FontSize="14" 
                           FontWeight="Bold" 
                           Margin="5,0,10,0" 
                           Width="{Binding RelativeSource={RelativeSource Mode=FindAncestor, 
                                                           AncestorType={x:Type Expander}}, Path=ActualWidth}" >
                    <TextBlock Text="{Binding Path=Name}" />
                    <Grid Width="10"/>
                        (
                        <TextBlock Text="{Binding Path=ItemCount}" /> 
                        items)
                </TextBlock>
            </Border>
        </Expander.Header>
        <Expander.Content>
            <ItemsPresenter />
        </Expander.Content>
    </Expander>
</ControlTemplate>

<ListView x:Name="datagridScenes" SelectionMode="Single"  >
    <ListView.GroupStyle >
        <GroupStyle HidesIfEmpty="False" >
            <GroupStyle.ContainerStyle >

                <!-- If I comment out this element, I loose the grouping, but the comboboxes work -->
                <Style TargetType="{x:Type GroupItem}" >
                    <Setter Property="Template" Value="{StaticResource SceneGroupItemTemplate}" />
                </Style>

            </GroupStyle.ContainerStyle>
        </GroupStyle>
    </ListView.GroupStyle>
</ListView>

public class AddressEntity : _EntityBase
{
    public AddressTypeEntity AddressType { get; set; }
    public string Street1 { get; set; }
    public string Street2 { get; set; }
    public string City { get; set; }
    public string State { get; set; }
    public string ZipCode { get; set; }
    public bool IsPrimary { get; set; }
    public string DisplayValue { get; set; }
}

public class AddressTypeEntity : _EntityBase
{
    public string Caption { get; set; }
}

<ComboBox x:Name="Types" 
            Grid.Row="2"
            Grid.Column="1"
            ItemsSource="{Binding AddressTypes}"
            SelectedItem="{Binding SelectedAddressType, Mode=TwoWay}"
            Margin="5,0,0,0"
            VerticalAlignment="Center"
            HorizontalAlignment="Left"
            FontFamily="Segoe UI"
            FontSize="14"
            Foreground="DarkSlateGray"
            Width="140">
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="{Binding Address.AddressType.Caption}"/>
            </StackPanel>
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>