Resource culture vaue automatically changing

Question

I am using resource files in my application. In base controller i am defining my application culture as follows

protected override IAsyncResult BeginExecuteCore(AsyncCallback callback, object state)
    {

        string cultureName = RouteData.Values["culture"] as string; 

        CultureInfo culture = null;


        HttpCookie cultureCookie = Request.Cookies["_culture"];
        if (cultureCookie != null)
            cultureName = "de-CH"; 
        else
            cultureName = "de-CH"; 
        // Validate culture name
        cultureName = CultureHelper.GetImplementedCulture(cultureName); 

        // Modify current thread's cultures            
        Thread.CurrentThread.CurrentCulture = new System.Globalization.CultureInfo(cultureName);
        Thread.CurrentThread.CurrentUICulture = Thread.CurrentThread.CurrentCulture;

        Thread.CurrentThread.CurrentCulture = CultureInfo.CreateSpecificCulture(cultureName);
        System.Globalization.CultureInfo.DefaultThreadCurrentCulture = Thread.CurrentThread.CurrentCulture;
        System.Globalization.CultureInfo.DefaultThreadCurrentUICulture = Thread.CurrentThread.CurrentCulture;      
        return base.BeginExecuteCore(callback, state);
    }

But at times the appication culture automatically changes to English if the system stays idle for few mintutes.

I tried to recreate the issue but its not alwats happening.

can anyone direct me why this is happening!

I havent set any expiry value for the culture.