title: ComboBox does not select binding value initially
body: <p>First of all, not a duplicate.</p>
  
  <p>TextBox and CheckBox work correctly, just not ComboBox.</p>
  
  <h3>Model</h3>
  
  <pre><code>internal class Word : _Model
  {
      public enum Categories
      {
          Noun,
          Verb,
      }
  
      private Categories category;
      public Categories Category
      {
          get
          {
              return this.category;
          }
          set
          {
              this.SetProperty(ref this.category,
                               value);
          }
      }
  }
  </code></pre>
  
  <h3>Notify (safe to skip reading this part)</h3>
  
  <pre><code>internal abstract class _Model : INotifyPropertyChanged
  {
      public event PropertyChangedEventHandler PropertyChanged;
  
      protected bool SetProperty&lt;T&gt;(ref T storage, T value, [CallerMemberName] string propertyName = null)
      {
          if (object.Equals(storage, value))
          {
              return false;
          }
          storage = value;
          this.OnPropertyChanged(propertyName);
          return true;
      }
  
      protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
      {
          var eventHandler = this.PropertyChanged;
          if (eventHandler != null)
          {
              eventHandler(this, new PropertyChangedEventArgs(propertyName));
          }
      }
  }
  </code></pre>
  
  <h3>Control (Model)</h3>
  
  <pre><code>public sealed partial class WordEditor : UserControl
  {
      public WordEditor()
      {
          this.Model = new Models.Word();
          this.Model.Category = Models.Word.Categories.Verb;
          this.InitializeComponent();
      }
  
      private Models.Word Model { get; set; }
  
      internal IList&lt;KeyValuePair&lt;Models.Word.Categories, string&gt;&gt; Categories { get { return new List&lt;KeyValuePair&lt;Models.Word.Categories, string&gt;&gt;() { new KeyValuePair&lt;Models.Word.Categories, string&gt;(Models.Word.Categories.Noun, "Noun"), new KeyValuePair&lt;Models.Word.Categories, string&gt;(Models.Word.Categories.Verb, "Verb") }; } }
  }
  </code></pre>
  
  <h3>Binding</h3>
  
  <pre><code>&lt;UserControl.Resources&gt;
      &lt;converters:AnyConverter x:Key="AnyConverter"/&gt;
  &lt;/UserControl.Resources&gt;
  
  &lt;StackPanel&gt;
      &lt;ComboBox ItemsSource="{x:Bind Path=Categories, Mode=OneTime}"
                DisplayMemberPath="Value"
                SelectedValuePath="Key"
                SelectedValue="{x:Bind Path=Model.Category, Mode=TwoWay, Converter={StaticResource ResourceKey=AnyConverter}}"/&gt;
  &lt;/StackPanel&gt;
  </code></pre>
  
  <h3>Converter</h3>
  
  <pre><code>internal class AnyConverter : IValueConverter
  {
      public object Convert(object value, Type targetType, object parameter, string language)
      {
          return value;
      }
  
      public object ConvertBack(object value, Type targetType, object parameter, string language)
      {
          return value;
      }
  }
  </code></pre>
  
  <h3>Issue</h3>
  
  <p>The ComboBox has "Verb" and "Noun" displayed correctly, and selection on "Verb" or "Noun" is reflected by the model correctly.</p>
  
  <p>However, even though Category is set to Verb at the very first place, the ComboBox does not show that.</p>
  
  <p>How to fix it so that the ComboBox selects "Verb" when it first appears?</p>