Caliburn.Micro Screen.CanClose() and MessageDialog().ShowAsync()

I'm currently using Caliburn.Micro 2.0 for my Windows Phone 8.1 project (Universal App) and I'm having problem with conditionally cancelling page close after user clicks a MessageDialog button.

It seems that Caliburn closes page after leaving CanClose() method, not waiting for the callback which is called after async MessageDialog.

public class MyViewModel: Screen
{
  public override async void CanClose(Action<bool> callback)
  {     
    MessageDialog dlg = new MessageDialog("Close?","Confirmation");
    dlg.Commands.Add(new UICommand() { Id = 0,  Label = "Yes" });
    dlg.Commands.Add(new UICommand() { Id = 1,  Label = "No"  });       

    var result = await dlg.ShowAsync();

    callback((int)result.Id == 0);  
  }
}

The only solution I have at the moment is set a field with a flag indicating if the page can be closed. On the user attempt to navigate back I tell Caliburn to abort the close and I display the confirmation dialog. When I get the result I set the flag to true and navigate back manually. This causes another call to CanClose, but this time I set the callback to true and skip the dialog part.

I don't like this solution much, but it is only way I managed to solve this problem.

private bool canClose = false;

public override async void CanClose(Action<bool> callback)
{
  callback(canClose);

  if (!canClose)
  {
    MessageDialog dlg = new MessageDialog("Close?","Confirmation");
    dlg.Commands.Add(new UICommand() { Id = 0,  Label = "Yes" });
    dlg.Commands.Add(new UICommand() { Id = 1,  Label = "No"  });       

    var result = await dlg.ShowAsync();

    if ((int)result.Id == 0)
    {
      canClose = true;
      navigationService.GoBack();
    }
  }
}

PS: I don't use MessageDialog directly in my ViewModel, I'm using a dialog service interface for popups. I just used it here to demonstrate the issue.