Comment 1 for bug 834942

On line 286, you have the code to set a variable named "deb". For some reason, the render function is not merging the code of the mako file, and the code of the ccs, header, and stuff. I modified the code as below, i don't have any idea if something is lost, but my report works. My report uses functions and they work. Try if it works for you. Still waiting for a pro answer.
if report_xml.webkit_debug :
            try :
                #deb = head_mako_tpl.render(helper=helper,
                # css=css,
                # _debug=tools.ustr("\n".join(htmls)),
                # _=self.translate_call,
                # **self.parser_instance.localcontext)
                deb = tools.ustr("\n".join(htmls)).encode('UTF-8')#Just commented all above, and set this deb
            except Exception, e:
                msg = exceptions.text_error_template().render()
                logger.error(msg)
                raise except_osv(_('Webkit render'), msg)
            return (deb, 'html')