title: Combobox SelectedItem not working as expected
body: <p>I have a combobox which binds to a collection of Foo on my viewmodel (<code>FooCollection</code>). I also set the <code>SelectedItem</code> property of the combobox to a property on my viewmodel of type <code>Foo</code> called <code>SelectedFoo</code></p>
  
  <p>I then set FooCollection and SelectedFoo and fire the appropriate OnPropertyChanged events.</p>
  
  <p>My combobox contains the list of Foo, but the item displayed in the combobox is always the first item in the list. However, if you drop down the combobox, the item that is then highlighted is the correct item (<code>SelectedFoo</code>). Therefore, it is selecting the correct item, but not displaying it.</p>
  
  
  
  <pre class="lang-xml prettyprint-override"><code>&lt;ComboBox Grid.Row="5"  ItemsSource="{Binding Path=FooCollection}" 
                           SelectedItem="{Binding SelectedFoo, Mode=TwoWay}" 
                           Name="FooSelectionControl"/&gt;
  </code></pre>
  
  <p>Does anyone know how to fix this?</p>