title: WPF ComboBox doesn't initially select correct item
body: <p>I have a WPF <code>ComboBox</code> that I bind to a list of custom objects, each of which contains an <code>IsSelected</code> property.  This property is bound to its corresponding <code>ComboBoxItem</code>'s <code>IsSelected</code> property.  When initially creating the list, I set a particular object's <code>IsSelected</code> property to <code>true</code>, with the expectation that this item will be selected when the ComboBox is initially shown.  However, the ComboBox always shows the first item in the list as selected, regardless of which object in its bound list has its <code>IsSelected</code> property set to <code>true</code>.  </p>
  
  <p>I know that the binding is working properly, because when I click the <code>ComboBox</code> and it expands to show all the available options, the <code>ComboBox</code> updates to show the correct selected item.</p>
  
  <p>Here's the XAML the defines my <code>ComboBox</code>.  It's in a <code>DataTemplate</code>, and is dynamically added/removed from the page, if that is at all relevant:</p>
  
  <pre><code>&lt;ComboBox ItemsSource="{Binding DataContext.YearList, RelativeSource={RelativeSource AncestorType=Window}}" IsSynchronizedWithCurrentItem="True"&gt;
    &lt;ComboBox.ItemContainerStyle&gt;
      &lt;Style TargetType="{x:Type ComboBoxItem}"&gt;
        &lt;Setter Property="IsSelected" Value="{Binding IsSelected}"/&gt;
      &lt;/Style&gt;
    &lt;/ComboBox.ItemContainerStyle&gt;
    &lt;ComboBox.ItemTemplate&gt;
      &lt;DataTemplate&gt;
        &lt;StackPanel Orientation="Horizontal"&gt;
          &lt;Label Content="{Binding Object}"/&gt;
        &lt;/StackPanel&gt;
      &lt;/DataTemplate&gt;
    &lt;/ComboBox.ItemTemplate&gt;
  &lt;/ComboBox&gt;
  </code></pre>