GZIP compression

[Zÿm]

protected void Application_PostReleaseRequestState(object sender, EventArgs e)
    {
        string contentType = Response.ContentType;

        if (contentType == "text/html" || contentType == "text/css" || contentType == "application/x-javascript" || contentType == "application/json")
        {
            Response.Cache.VaryByHeaders["Accept-Encoding"] = true;
            string acceptEncoding = Request.Headers["Accept-Encoding"];

            if (acceptEncoding != null)
            {
                if (acceptEncoding.Contains("gzip"))
                {
                    Response.Filter = new GZipStream(Response.Filter, CompressionMode.Compress);
                    Response.AppendHeader("Content-Encoding", "gzip");
                }
                else if (acceptEncoding.Contains("deflate"))
                {
                    Response.Filter = new DeflateStream(Response.Filter, CompressionMode.Compress);
                    Response.AppendHeader("Content-Encoding", "deflate");
                }
            }
        }
    }

I got this code in global.asax, i want gzip enabled, but not on iis level, but after this, radDateTimePicker is broken.
it still "works" but it has no style, pick button is repeated in strange way, and the title of hyperlink is shown instead of image button; Am i doing something wrong?