[wicket 6] javascript confirmation via onPrecondition failed.

[smallufo]

I want to add a warning dialog when user clicks an ajax "deleteLink"
I saw the following solution:

    Link<Void> deleteLink = new AjaxFallbackLink<Void>("deleteLink")
    {
      @Override
      public void onClick(AjaxRequestTarget target)
      {
        commentService.deleteComment(user, comment, ip);
        setResponsePage(CommentsPage.class , pps);
      }

      @Override
      protected void updateAjaxAttributes(AjaxRequestAttributes attributes)
      {
        super.updateAjaxAttributes(attributes);

        AjaxCallListener ajaxCallListener = new AjaxCallListener();
        ajaxCallListener.onPrecondition("return confirm('Are you sure?');");
        attributes.getAjaxCallListeners().add(ajaxCallListener);
      }
    };
    add(deleteLink);

It did popup a warning box , display "Are you sure?"
But no matter user clicks OK or Cancel
The comment get deleted !

What's wrong here ?

Thanks.

(wicket 6.7)