Problem with TabbedPage and CarouselPage

I have a strange problem with both types of pages. Whenever I set CurrentPage in code they lock that page. ie, when I click on another tab it switches to the new tab but immediately switches back to the one I set in code. Eg, in the xaml.cs

private void GotoView(string name)
{
  CurrentPage = AssignmentLinesView;
  // CurrentPage = null;
}

private void AssignmentView_OnCurrentPageChanged(object sender, EventArgs e)
{
  var p = CurrentPage;
  Debug.WriteLine("CurrentPage " + p.GetType().Name);
}

The GotoView is called from the message centre subscribe. I call it from the VM.

Also, in the CarouselPage, when GotoView is called it doesn't display the contents of the view, the TabbedPage does.