title: PageExpiredException occurs after closing of ModalWindow
body: <p><br/>
  Currently I'm trying to upgrade the application from wicket 1.4 to wicket 6 and I'm stuck with the following issue:
  <br/>
  When I try to close <code>ModalWindow</code>, it is closed but I receive <code>PageExpiredException</code> on the page where I was opening this <code>ModalWindow</code>, so I'm redirected to 
  /myapp/wicket/bookmarkable/org.apache.wicket.markup.html.pages.PageExpiredErrorPage
  <br/>
  I thought maybe the way I create <code>ModalWindow</code> is outdated, so I've tried an example from here</p>
  
  <blockquote>
    <p><a href="http://www.wicket-library.com/wicket-examples-6.0.x/ajax/modal-window?0" rel="nofollow">http://www.wicket-library.com/wicket-examples-6.0.x/ajax/modal-window?0</a>
    <br/></p>
  </blockquote>
  
  <p>and it gives me the same exception.</p>
  
  <p>Maybe I have to configure something in my <code>WebApplication</code> implementation, but I don't know what.
  If anyone could help, it'll be really appreciated. Thanks.</p>