The editor.js does not build urls correctly if you are running a web server on anything other than port 80.
Fix by replacing the first line of js with this:
var port = (window.location.port == 80) ? '' : ':' + window.location.port;
var url = window.location.protocol + '//' + window.location.hostname + port + window.location.pathname + '?<%hidden_query%>';
Fix by replacing the first line of js with this:
var port = (window.location.port == 80) ? '' : ':' + window.location.port;
var url = window.location.protocol + '//' + window.location.hostname + port + window.location.pathname + '?<%hidden_query%>';