title: Combobox' SelectedItem bound to a DependencyProperty is not refreshing
body: <p>I have a combobox, whose SelectedItem is bound to a dependency property.</p>
  
  <pre><code>public IEnumerable&lt;KeyValuePair&lt;int,string&gt;&gt; AllItems
  {
      get { return _AllItems; }
      set
      {
          _AllItems = value;
          this.NotifyChange(() =&gt; AllItems);
      }
  }
  
  public KeyValuePair&lt;int, string&gt; SelectedStuff
  {
      get { return (KeyValuePair&lt;int, string&gt;)GetValue(SelectedStuffProperty); }
      set
      {
          SetValue(SelectedStuffProperty, value);
          LoadThings();
      }
  }
  
  public static readonly DependencyProperty SelectedStuffProperty =
      DependencyProperty.Register("SelectedStuff", typeof(KeyValuePair&lt;int, string&gt;), typeof(MyUserControl), new UIPropertyMetadata(default(KeyValuePair&lt;int, string&gt;)));
  </code></pre>
  
  <p>And the xaml:</p>
  
  <pre><code>&lt;ComboBox DisplayMemberPath="Value"
            ItemsSource="{Binding AllItems}"
            SelectedItem="{Binding SelectedStuff, Mode=TwoWay}" /&gt;
  </code></pre>
  
  <p>The data is correctly bound and displayed, but when I select another value in the combobox, the <code>set</code> is not called, neither is my <code>LoadThings()</code> method called.</p>
  
  <p>Is there an obvious reason ?</p>
  
  <p>Thanks in advance</p>
  
  <hr>
  
  <h1>Edit</h1>
  
  <p>I used snoop to view inside the combobox, and when I change the value, the combobox' SelectedItem is also changed.<br>
  I also checked in the code, and the property is changed.  But my method is not called (as I don't go through the <code>set</code>, so the problem is still there...</p>