title: adding an object to an ObservableCollection makes two UI items appear
body: <p>I made a simple test app where I have a MvxLinearLayout with ItemSource bound to an ObservableCollection of string values. The item template is a TextView.</p>
  
  <p>On a Button I add a new string to the collection. In the UI there are two items added.</p>
  
  <p>I am using latest MVVMCross from NuGet, and running under Debug with Linker set to 'Don't Link'</p>
  
  <p>I uploaded the source code of the app here:
  <a href="http://sdrv.ms/13l9dnR" rel="nofollow">http://sdrv.ms/13l9dnR</a></p>