estou usandoJava EE 5, EJB 3.0, Jboss AS 4.3.2.
Eu tenho mais simplesStateful feijão

@Local
public interface IStateBean 
{
}
@Stateful
public class StateBean implements IStateBean
{  
   private static int number = 0;

   @PostConstruct
   void init()
   {
      number++;
      System.out.println("@PostConstruct: " + number);
   }

   @PreDestroy
   void destroy()
   {
      number--;
      System.out.println("@PreDestroy: " + number);  
   }
}

Eu procuro no servlet para este bean

public class MyServlet extends HttpServlet
{  
   @Override
   public void doGet(final HttpServletRequest aRequest, final HttpServletResponse aResponse) throws ServletException, IOException
   {  
      IStateBean bean = new InitialContext().lookup("app-ear/StateBean/local");
      // ...
   }
}  

Mas cada vez nova instância deStateBean é criado.
eu posso ligarlookup duas vezes, mas nova instância deStateBean é criado novamente

   @Override
   public void doGet(final HttpServletRequest aRequest, final HttpServletResponse aResponse) throws ServletException, IOException
   {  
      IStateBean bean1 = new InitialContext().lookup("app-ear/StateBean/local"); 
      IStateBean bean2 = new InitialContext().lookup("app-ear/StateBean/local"); // new instance is created
      // ...
   }  

Espero que a mesma instância na mesma sessão http

Mapeamento de servlet no web.xml

   <servlet>
      <servlet-name>MyServlet</servlet-name>
      <servlet-class>com.package.MyServlet</servlet-class>
   </servlet>  
   <servlet-mapping>
      <servlet-name>MyServlet</servlet-name>
      <url-pattern>*.html</url-pattern>
   </servlet-mapping>