#5167 remove callback once loaded

@@ -10,6 +10,9 @@ define([], function() {
             request.onreadystatechange = function() {
                 if (request.readyState == 3 || request.readyState == 4) {
                     if (request.status == 200){
+                        if (request.onreadystatechange) {
+                            request.onreadystatechange = null;
+                        }
                         if (request.responseText) {
                             var newText = request.responseText.substr(responseLength);
                             if (newText.length > 0) {