按下窗口按钮后恢复时的导航问题-WP8.1 C#

WP8.1 Silverlight应用程序

我已经设置了一个urimapper，可以根据不同的条件启动不同的页面。在应用程序构造函数中调用函数SetUriMapper

应用程序xaml

<UriMapper:UriMapper x:Name="mapper">
    <UriMapper:UriMapping Uri="/RootPage.xaml" />
</UriMapper:UriMapper>

应用程序.xaml.cs

    public App()
    {
        // Global handler for uncaught exceptions. 
        UnhandledException += Application_UnhandledException;
        // Standard Silverlight initialization
        InitializeComponent();
        // Phone-specific initialization
        InitializePhoneApplication();
       // Database functions
        SetupUriMapper();
   }
    void SetupUriMapper()
    {
        // Get the UriMapper from the app.xaml resources, and assign it to the root frame
        UriMapper mapper = Resources["mapper"] as UriMapper;
        RootFrame.UriMapper = mapper;

       if (condition)
       {
           mapper.UriMappings[0].MappedUri = new Uri("/Walkthrough.xaml",       UriKind.Relative);
       }
       else if (condition2)
       {
           mapper.UriMappings[0].MappedUri = new Uri("/ResetPasswordPrompt.xaml", UriKind.Relative);
       }
       else 
           mapper.UriMappings[0].MappedUri = new Uri("/MainPage.xaml", UriKind.Relative);
     }

    private void Application_Activated(object sender, ActivatedEventArgs e)
    {
            // reading data from database
            CycleManager cycMan = CycleManager.Instance;
            using (DBManager dbMan = new DBManager())
            {
                dbMan.OpenConnection();
                dbMan.ReadSettingsData(cycMan.ActiveAccount);
            }
    }

现在用户已进入页面B，并按下主页按钮。然后转到应用程序列表，再次选择该应用程序。调用Application_Activated并将其导航到页面B。但不到一秒钟，它就导航回MainPage。

但是，如果用户按下后退按钮继续，它会导航到页面B并停留在那里。

行为很奇怪，有线索吗？