title: ObservableCollection's CollectionChanged not firing
body: <p>I have an <code>ObservableCollection</code>, based on <code>List</code>.</p>
  
  <pre><code>private List&lt;int&gt; markers = new List&lt;int&gt;();
  private ObservableCollection&lt;int&gt; markersObservable;
  
  markersObservable = new ObservableCollection&lt;int&gt;(markers);
  markersObservable.CollectionChanged += MarkersObservable_CollectionChanged;
  </code></pre>
  
  <p>When adding element into the list:</p>
  
  <pre><code>markers.Add(hScrollBarPoints.Value);
  </code></pre>
  
  <p>I expect collection changed event would fire, however, event never fired:</p>
  
  <pre><code>private void MarkersObservable_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
  {
      Console.WriteLine("Changed!");
  }
  </code></pre>
  
  <p>What am I doing wrong?</p>