The following servlet will generate an HTTP response with two Content-Type 
headers and two Content-Length headers.

    import javax.servlet.http.*;

    public class HeaderBug extends HttpServlet {
        protected void doGet(HttpServletRequest request, HttpServletResponse 
response) {
            response.setHeader("Content-Type", "text/xml");
            response.setContentType("text/html");
            response.setIntHeader("Content-Length", 200);
            response.setContentLength(100);
        }
    }

It looks like the way HttpResponseBase.setHeader() HttpResponseBase.sendHeaders
() are treating these two headers doesn't play well with 
ResponseBase.setContentType() and ResponseBase.setContentLength().