奇怪的session混乱问题

   服务器:jboss4.2
   问题:偶尔两个帐号在两台不同的机器上,a帐户获取了b帐号的session值
  

public ActionForward loadDialogList4Inbox(ActionMapping mapping,
            ActionForm form,
            HttpServletRequest request,
            HttpServletResponse response)throws Exception{
        MailService service = (MailService)this.getBean("mailService");
        List labels = (List)request.getSession().getAttribute("labels");
        if(labels == null){
            labels = service.loadLabelWithTotal(this.getUserId());
            request.getSession().setAttribute("labels",labels);
        }
        return mapping.findForward("dialogList");
  }