title: ReactiveUI and DynamicData SourceCache update issue
body: <p>I am using SouceCache from DynamicData in my Xamarin Forms project to track changes from the backend. First I am getting the list of Items from backend, populate the UI and then wait for changes.</p>
  
  <p>The issue is that when new(updated) object arrives from backend, I find and update it in an _innerCache collection, there is no new value emitted from observable, and UI is not updated.</p>
  
  <p>Code is simplified but it is something like this:</p>
  
  <pre><code>_internalSourceCache = new SourceCache&lt;Item, string&gt;(o =&gt; o.Id);
  
  public IObservable&lt;IChangeSet&lt;Item, string&gt;&gt; Connect() =&gt; _internalSourceCache.Connect();
  
  private void OnItemUpdated(List&lt;Item&gt; items)
          {
              foreach (var item in items)
              {
                  _internalSourceCache.Edit(innerCache =&gt;
                  {
                      innerCache.AddOrUpdate(item);
                  });
              }
          }
  </code></pre>
  
  <p>And in a view model where I need those changes:</p>
  
  <pre><code>itemsService
       .Connect()
       .Transform(item=&gt;
             {
  
                 return new ItemCellViewModel(item);
             }, (_, n) =&gt; _ = new ItemCellViewModel(n))
       .Sort(SortExpressionComparer&lt;ItemCellViewModel&gt;.Descending(t =&gt; t.Status))
       .DisposeMany()
       .ObserveOn(MainThreadScheduler)
       .Bind(out _items)
       .Subscribe();
  </code></pre>
  
  <p>I am obviously missing something, but I still don't know what, so please help if you see the problem :)</p>