This is because we are connecting to configure-event of parent window, but not returning FALSE from the callback to propagate the event.
Created attachment 383267 [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 r252355: <https://trac.webkit.org/changeset/252355>