Xamarin.Forms 1.3.x on WinPhone crashes when hardware back button is pressed

Hi There,

We had been using Xamarin.Forms 1.2.3 and everything was working well. Now while we're trying to upgrade to the latest version of Xamarin.Forms, we are coming across this issue on Windows phone that it keeps crashing giving the following error:

System.InvalidOperationException: Sequence contains no elements
   at System.Linq.Enumerable.Last[TSource](IEnumerable`1 source)
   at Xamarin.Forms.Platform.WinPhone.Platform.OnBackKeyPress(Object sender, CancelEventArgs e)
   at System.EventHandler`1.Invoke(Object sender, TEventArgs e)
   at Microsoft.Phone.Controls.PhoneApplicationPage.Microsoft.Phone.Controls.IPhoneApplicationPage.InternalOnBackKeyPress(CancelEventArgs e)
   at System.Windows.Navigation.Journal.SystemKeyPressed(NavigationSystemKey systemKeyType)
   at Microsoft.Phone.TaskModel.Interop.Task.FireOnSystemKeyPressed(Int32 systemKeyType)

We're not sure what it is that's causing this issue.

Any guidance for a fix or a workaround is appreciated.

Thanks.