WebMarkupMin: Minification not working for pages with response code !=200

Hello, when i am using minification on 404 or other custom error pages, its totally ignored if i set HttpContext.Response.StatusCode=404; you can check the live url here ultrawebz

[CompressContent]
    [MinifyHtml]
    [MinifyXml]
public ActionResult HttpError404(string message="")
        {
            //HttpContext.Response.StatusCode=404; minification works only after this commented
            ViewBag.msg = message;
            return View();          
        }

but commenting this code is bad practice for seo. i am using webmarkupmin ver 2.5.7 (core) WebMarkupMin.AspNet4.Mvc 2.5.0

regards