[Wicket-user] Problem with the basics?

[Crash_neo]

I'm having trouble with a very simple file.
For the record this works on wicket 1.1
I am now using wicket head.
If you run the attached files on HEAD you get this Error:
  

java.lang.RuntimeException: Internal error cloning object
        wicket.Session.setAttribute(Session.java:838)
        wicket.Session.update(Session.java:892)
        wicket.protocol.http.WebSession.update(WebSession.java:282)
        wicket.RequestCycle.cleanUp(RequestCycle.java:797)
        wicket.RequestCycle.steps(RequestCycle.java:1067)
        wicket.RequestCycle.request(RequestCycle.java:534)
        wicket.protocol.http.WicketServlet.doGet(WicketServlet.java:199)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

on a tomcat 5.5.9 webserver

If you remove the FORM it works fine.

It breaks on 
line 833:    new ObjectOutputStream(out).writeObject(value);


Is this an error occurred by the 1.1 -> 1.2 migration,  thus am I doing 
something wrong?
Or is it really an error?

Cheers  Thijs








  
    UserId: Message goes here
    username: Message goes here
    
      UserId: 
      UserName: 
      
      
    
  


import wicket.markup.html.WebPage;
import wicket.markup.html.basic.Label;
import wicket.markup.html.form.Form;
import wicket.markup.html.form.TextField;
import wicket.model.PropertyModel;

public class Index2 extends WebPage{

  public Index2(){
    User user = new User();
    add(new Label("userId", new PropertyModel(user, "userId")));
    add(new Label("userName", new PropertyModel(user, "userName")));
    add(new UserForm("userInputForm", user));
  }
  private final class UserForm extends Form
  {
    public UserForm(String id, User user)
    {
      super(id);
      add(new TextField("userIdInput", new PropertyModel(user, "userId")));
      add(new TextField("userNameInput", new PropertyModel(user, "userName")));
    }
    protected void onSubmit(){}
  }
  
  private class User{
    int userId = 200;
    String userName = "Thijs";
    public User(){}
    
    public int getUserId() {  return userId;  }
    
    public void setUserId(int userId) {  this.userId = userId;  }

    public String getUserName() {   return userName;  }

    public void setUserName(String userName) {  this.userName = userName;  }
    
  }

}