title: New shell/window in Prism/WPF shows wrong view
body: <p>Inspired by <a href="https://stackoverflow.com/a/5280281/487356">this answer</a>, I created a general purpose Shell (Prism, WPF) like this:</p>
  
  <pre><code>&lt;Window x:Class="VRMDataLogger.UI.Shell" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:prism="http://prismlibrary.com/" Title="My App" Height="450" Width="800"&gt;
      &lt;Grid&gt;
          &lt;ContentControl prism:RegionManager.RegionManager="{Binding RegionManager}" prism:RegionManager.RegionName="MainShellRegion" /&gt;
      &lt;/Grid&gt;
  &lt;/Window&gt;
  </code></pre>
  
  <pre><code>public partial class Shell : Window
  {
      public Shell(IRegionManager regionManager, Type contentType)
      {
          RegionManager = regionManager;
          InitializeComponent();
          RegionManager.RegisterViewWithRegion("MainShellRegion", contentType);
      }
  
      public IRegionManager RegionManager { get; }
  }
  
  </code></pre>
  
  <p>The initial shell gets created in <code>App.CreateShell()</code>:</p>
  
  <pre><code>protected override Window CreateShell()
  {
      return new Shell(Container.Resolve&lt;IRegionManager&gt;(), typeof(StartScreen));
  }
  </code></pre>
  
  <p>This works fine and the correct view is shown in that initial shell.</p>
  
  <p>I then try to create a second Shell from <code>StartScreenViewModel</code> which shows a different view:</p>
  
  <pre><code>var shell = new Shell(RegionManager.CreateRegionManager(), typeof(MainScreen));
  shell.Show();
  </code></pre>
  
  <p>This opens a new window, but it shows the same view like the first window (<code>StartScreen</code>) instead of <code>MainScreen</code>. What am I doing wrong here?</p>