Consider this example. The post request is successful.

QNetworkReply* reply = qNetworkAccessManager->post(request, data);
qDebug() << "error" << reply->error();
qDebug() << "errorString" << reply->errorString();

 
Observed:
The error and errorString differs. The errorString reports an unknown error.

error: QNetworkReply::NoError
errorString: "Unknown error"

 
 
Expected:
I would expect that error and errorString match, i.E. if error says there is no error than the errorString shall not report an unknown error.