title: Navigation corrupted - ViewModel can't close?
body: <p>On every other place the navigation just works fine, only on this place it doesnt work (it's set up like all the other Viewmodels)</p>
  
  <p>I'm trying to navigate from ImportView (ImportViewModel) to the LoginView (LoginViewModel). 
  On Buttonclick (Binded MvxCommand in ViewModel) I'm calling <code>ShowViewModel&lt;LoginViewModel&gt;();</code></p>
  
  <p>Its working but afterwards the whole navigation is broken. If I move now from the newly opened LoginViewModel to for Example TestViewModel (or TestView), and now going "Back", I'm not coming to the LoginView back, instead to a BlackScreen and there is one more "Back", after that the App crashes... (<code>MonoTouch.Foundation.MonoTouchException: Objective-C exception thrown.  Name: NSInvalidArgumentException Reason: Can't add self as subview</code>)</p>
  
  <p>Where is here the Problem?</p>
  
  <p>Here some Debuginformations:</p>
  
  <pre><code>[0:] mvx:Warning: 26.41 Don't know how to close this viewmodel - topmost view does not present this viewmodel
  [0:] 
  2013-12-13 13:19:28.400 INMobileAdminUIiOS[6932:60b] mvx:Diagnostic: 26.81 Showing ViewModel LoginViewModel
  [0:] mvx:Diagnostic: 26.81 Showing ViewModel LoginViewModel
  [0:] 
  2013-12-13 13:19:28.799 INMobileAdminUIiOS[6932:60b] TouchNavigation:Diagnostic: 27.21 Navigate requested
  [0:] TouchNavigation:Diagnostic: 27.21 Navigate requested
  2013-12-13 13:19:29.085 INMobileAdminUIiOS[6932:60b] nested push animation can result in corrupted navigation bar
  [0:] 
  2013-12-13 13:19:29.224 INMobileAdminUIiOS[6932:601f] 13.12.2013 13:19:29   TinyMessage: ProgressDialogDismissMessage
  [0:] 13.12.2013 13:19:29    TinyMessage: ProgressDialogDismissMessage
  2013-12-13 13:19:29.463 INMobileAdminUIiOS[6932:60b] Finishing up a navigation transition in an unexpected state. Navigation Bar subview tree might get corrupted.
  </code></pre>