title: Dependecy Property works as source but not as target
body: <p>I have a dependency property in a user control.</p>
  <pre><code>    public ComputerListView()
      {
          InitializeComponent();
  
          vm = new ComputerViewModel();
  
          this.DataContext = vm;
  
          DispatcherTimer time = new DispatcherTimer(TimeSpan.FromSeconds(1), DispatcherPriority.Normal,
              delegate
              {
                    SetValue(AutoCounterProperty, vm.SimpleCounter);
              },
              Dispatcher);
  
      }
  
      public int AutoCounter
      {
          get { return (int)GetValue(AutoCounterProperty); }
          set { SetValue(AutoCounterProperty, value); }
      }
  
      // Using a DependencyProperty as the backing store for Counter.  This enables animation, styling, binding, etc...
      public static readonly DependencyProperty AutoCounterProperty =
          DependencyProperty.Register(&quot;AutoCounter&quot;, typeof(int), typeof(ComputerListView), new PropertyMetadata(0));
      }
  
  &lt;StackPanel&gt;
      &lt;local:ComputerListView x:Name=&quot;computerListView&quot; AutoCounter=&quot;{Binding VMCounter, Mode=TwoWay}&quot;/&gt;
      &lt;TextBox Background=&quot;Beige&quot; Text=&quot;{Binding VMCounter, Mode=TwoWay}&quot;/&gt;
      &lt;TextBlock Background=&quot;LightCyan&quot; Text=&quot;{Binding ElementName=computerListView, Path=AutoCounter}&quot;/&gt;
      &lt;Button Content=&quot;VMCounter&quot; Click=&quot;VMCounter_Button_Click&quot;/&gt;
  &lt;/StackPanel&gt;
  </code></pre>
  <p>I expect that the <code>VMCounter</code> property will get updated as the <code>AutoCounter</code> will run in dependency property and the TextBox will be updated from the <code>VMCounter</code> property but it shows 0, never gets updated.</p>
  <p>I have use the <code>AutoCounter</code> the way I have in TextBlock, then it updates fine.</p>
  <p>I thought the major use of DP is to be able to used as target property like in first case. Why it doesn't work that way?</p>