Tombstoning working, but does my app need it?

Question

I am using the Tombstone helper from Codeplex and I am a bit confused, I thought that it saves the state of your app's controls i.e Textbox, and I use the code on one page of my app and don't use it on another page, but when I test it it just saves the state of the Textboxes in both pages the same, the Textbox without the Tombstone Helper attached when I test it keeps it's state. The way I am testing is pressing the Windows logo on the emulator opening the browser and then keeping the back button pressed.

this is the code I am using for Tombstoning

protected override void OnNavigatingFrom(System.Windows.Navigation.NavigatingCancelEventArgs e)
{
    this.SaveState(e); 
}

protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
    this.RestoreState();
}

I would appreciate if you could help me