title: UI not updating PropertyChanged with MVVM
body: <p>Is it ever possible that UI skips updating itself although the Visibility of the UI component is binded to ViewModel property and PropertyChanged for that property is implemented? </p>
  
  <p>View/XAML: </p>
  
  <pre><code> &lt;Border Visibility="{Binding ShowLoadingPanel, Converter={StaticResource BoolToHiddenConverter}}"&gt;
        &lt;TextBlock Text="LOADING..." /&gt;
   &lt;/Border&gt;
  </code></pre>
  
  <p>ViewModel: </p>
  
  <pre><code>Public Property ShowLoadingPanel As Boolean
      Get
          Return _showLoadingPanel
      End Get
      Set(value As Boolean)
          _showLoadingPanel = value
          OnPropertyChanged("ShowLoadingPanel")
      End Set
  End Property
  </code></pre>
  
  <p>When running the following from ViewModel:</p>
  
  <pre><code> ShowLoadingPanel = True
   RunBigTask()  'runs a task that takes a long time
   ShowLoadingPanel = False
  </code></pre>
  
  <p>...the Border defined in XAML doesn't become visible.</p>
  
  <p>But if I add something requiring user interaction, for example like:</p>
  
  <pre><code> ShowLoadingPanel = True
   MsgBox("Click to continue")
   RunBigTask()  'runs a task that takes a long time
   ShowLoadingPanel = False
  </code></pre>
  
  <p>... then the border becomes visible as desired.</p>
  
  <p>How is that possible?</p>