(Security Multi-user Client Problem) Bad remote CallerPrincipal when connecting 2 users from my client.

Hi,
I have a very annoying issue with my secured Glassfish 3.1.2.
When I connect 2 (or more) users from my EJB client, I am having always the last connected user when I do this in my EJB: sessionContext.getCallerPrincipal().getName();

Could you please give me a help on this issue?

Here is my client:

public static void main(String[] args) {
	new Thread(new Runnable() {
  @Override
  public void run() {
     connectUser("userA", "pwdB");
  }
	}).start();

	new Thread(new Runnable() {
           @Override
   public void run() {
        connectUser("userB", "pwdB");
   }
	}).start();
}

public static void connectUser(String userName, String password) {
 try {
     ProgrammaticLogin login = new ProgrammaticLogin();
     login.login(userName, password.toCharArray());
     Context context = new InitialContext();
     MyServiceRemote myService = (MyServiceRemote) context.lookup("MyService");
     String remoteCaller = myService.getUserName();
     System.out.println("Local is (" + userName + "), Remote is (" + remoteCaller + ")");
  } catch (Exception e) {
     e.printStackTrace();
  }
}

Here is my EJB:

@Stateless(mappedName = "MyService", name="MyServiceBean")
public class MyServiceBean implements MyServiceRemote{
	@Resource
	private SessionContext sessionContext;
	public MyServiceBean () {
		super();		
	}
	public String getUserName() {
		return sessionContext.getCallerPrincipal().getName();
	}
}