title: Wicket Label not updated / remains invisible
body: <p>I am trying to implement Breadcrumb Navigation on a <code>WebPage</code> that exchanges a content <code>Panel</code> via ajax.  </p>
  
  <p>It ends up looking like this:
  <code>Home &gt;&gt; Page &gt;&gt; Panel</code></p>
  
  <p>Here is my page code:</p>
  
  <pre><code>public MyPage() {
      super();
      contentContainer = new WebMarkupContainer("contentContainer");
      contentContainer.setOutputMarkupId(true);
      add(contentContainer);
      contentContainer.add(content = createContentPanel());   
  
      breadCrumbContainer = new WebMarkupContainer("breadcrumbContainer");
      breadCrumbContainer.setOutputMarkupId(true);
      add(breadCrumbContainer);   
  
      final AjaxLink panelLink = new AjaxLink("panelLink") {
  
          @Override
          public void onClick(final AjaxRequestTarget target) {
              replaceContentPanel(getOverviewPanel(), target);
          }
  
          @Override
          public boolean isVisible() {
              return !(content instanceof OverviewPanel);
          }
      };
      breadCrumbContainer.add(panelLink);
      panelLink.add(new Label("panelLabel", new Model&lt;String&gt;() {
          @Override
          public String getObject() {
              //some dynamic content for example:
              return contentPanel.getClass().getName();
          }
      }));  
  }
  
  public void replaceContentPanel(final Component replacer, final AjaxRequestTarget target) {
      content.replaceWith(replacer);
      content = replacer;
       if (target != null) {           
          target.add(contentContainer);
          target.add(breadCrumbContainer);
      }
  }
  </code></pre>
  
  <p>The Home and Page <code>Label</code> are easy. The one for Panel needs to be updated everytime I updated the content <code>Panel</code> of the <code>WebPage</code>. I was sure that the  <code>target.add(breadCrumbContainer);</code> line was going to do this. However it is empty. The Label shows nothing. </p>
  
  <p>I was hoping to find the answer - which is probably obvious - while writing up the question, but it still eludes me, so I am hoping someone here spots my mistake. </p>