title: WPF items not visible when grouping is applied
body: <p>I'm having this strange issue with my ItemsControl grouping. I have the following setup:</p>
  
  <pre><code>&lt;ItemsControl Margin="3" ItemsSource="{Binding Communications.View}" &gt;
      &lt;ItemsControl.GroupStyle&gt;
          &lt;GroupStyle&gt;
              &lt;GroupStyle.ContainerStyle&gt;
                  &lt;Style TargetType="{x:Type GroupItem}"&gt;
                      &lt;Setter Property="Template"&gt;
                          &lt;Setter.Value&gt;
                              &lt;ControlTemplate TargetType="{x:Type GroupItem}"&gt;
                                  &lt;Expander&gt;
                                      &lt;Expander.Header&gt;
                                          &lt;Grid&gt;
                                              &lt;Grid.ColumnDefinitions &gt;
                                                  &lt;ColumnDefinition Width="*" /&gt;
                                                  &lt;ColumnDefinition Width="Auto" /&gt;
                                              &lt;/Grid.ColumnDefinitions&gt;
                                              &lt;TextBlock Text="{Binding ItemCount, StringFormat='{}[{0}] '}" FontWeight="Bold" /&gt;
                                              &lt;TextBlock Grid.Column="1" Text="{Binding Name, Converter={StaticResource GroupingFormatter}, StringFormat='{}Subject: {0}'}" FontWeight="Bold" /&gt;
                                          &lt;/Grid&gt;
                                      &lt;/Expander.Header&gt;
                                      &lt;ItemsPresenter /&gt;
                                  &lt;/Expander&gt;
                              &lt;/ControlTemplate&gt;
                          &lt;/Setter.Value&gt;
                      &lt;/Setter&gt;
                  &lt;/Style&gt;
              &lt;/GroupStyle.ContainerStyle&gt;
          &lt;/GroupStyle&gt;
      &lt;/ItemsControl.GroupStyle&gt;
      &lt;ItemsControl.ItemTemplate&gt;
          &lt;DataTemplate&gt;
              &lt;Grid&gt;
                  &lt;Grid.ColumnDefinitions&gt;
                      &lt;ColumnDefinition Width="Auto" /&gt;
                      &lt;ColumnDefinition Width="*" /&gt;
                      &lt;ColumnDefinition Width="Auto" /&gt;
                  &lt;/Grid.ColumnDefinitions&gt;
                  &lt;Grid.RowDefinitions&gt;
                      &lt;RowDefinition /&gt;
                      &lt;RowDefinition /&gt;
                  &lt;/Grid.RowDefinitions&gt;
                  &lt;TextBlock FontWeight="Bold" Text="{Binding Inspector, Converter={StaticResource NameFormatter}, StringFormat='{}From {0}:'}" Margin="3" /&gt;
                  &lt;TextBlock Text="{Binding SentDate, StringFormat='{}{0:dd/MM/yy}'}" Grid.Row="1" Margin="3"/&gt;
                  &lt;TextBlock Text="{Binding Message }" Grid.Column="1" Grid.RowSpan="2" Margin="3"/&gt;
                  &lt;Button Command="vm:CommunicationViewModel.DeleteMessageCommand" CommandParameter="{Binding}"  HorizontalAlignment="Right" Grid.Column="2"&gt;Delete&lt;/Button&gt;
              &lt;/Grid&gt;
          &lt;/DataTemplate&gt;
      &lt;/ItemsControl.ItemTemplate&gt;
  &lt;/ItemsControl&gt;
  </code></pre>
  
  <p>In my ViewModel, I expose a CollectionViewSource named 'Communications'. I proceed to adding a grouping patter like so:</p>
  
  <pre><code>Communications.GroupDescriptions.Add(new PropertyGroupDescription("Subject"));
  </code></pre>
  
  <p>Now, the problem i'm experience is the grouping work fine, but I can't see any items inside the groups. What am I doing wrong? Any pointers would be much appreciated.</p>