The problem is that we don't send the window ID again to the new web process.
Created attachment 255915 [details]
Thanks for the patch. If this patch contains new public API please make sure it follows the guidelines for new WebKit2 GTK+ API. See http://trac.webkit.org/wiki/WebKitGTK/AddingNewWebKit2API
Committed r186221: <http://trac.webkit.org/changeset/186221>