I could not able to see this patch in the core.js
which is in the github. But I added the below thing in my strophe.js
and found that it is still incorrect.
//req.xhr.open("POST", this.service, true); //commented this line
var async = !('sync' in this && this.sync === true);//added this line
req.xhr.open("POST", this.service, async);
Please tell me If I am wrong and also help to how I can add this functionality.