title: ObservableCollection loses binding when I "new" it
body: <p>I have a ListBox on my UI that is bound to a property of ObservableCollection.  I set a new instance of the ObservableCollection into the property in the view model's constructor and I can add items to it with a button on the form.  These are visible in the list.</p>
  
  <p>All is good.</p>
  
  <p>However, if I reinitialize the property with <em>new</em> in the button callback, it breaks the binding and the UI no longer shows what is in the collection.</p>
  
  <p>I assumed the binding would continue to look up the values of the property, but its presumably linked to a reference which is destroyed by the <em>new</em>.</p>
  
  <p>Have I got this right?  Can anyone expand on how this is linked up?  Is there a way to rebind it when my view model has no knowledge of the view?</p>