QNetworkAccessManager POST request fails

Since we upgraded from 5.4.1 to 5.4.2 we have a networking issue performing POST of "big" files (> 3MB) using QNetworkAccessManager.

What happens is that the POST is started and once first chunk of data is sent to the server and the uploadProgress signal is correctly fired, nothing more happens, the POST task seems to be lost into Nirvana (or hanging) until the the timeout error occurs.

QNetworkRequest req;
req.setUrl(url);
req.setRawHeader("Accept", "application/json");
req.setHeader(QNetworkRequest::ContentLengthHeader, contentLength);
req.setHeader(QNetworkRequest::ContentTypeHeader, QVariant("application/octet-stream"));
QNetworkReply *reply = _networkAccessManager->post(req, customQIODevice);
// Signal wiring...

Downgrade back to 5.4.1 version fixes the issue.

Maybe this relates to QNAM patch of April 10th? http://code.qt.io/cgit/qt/qtbase.git/commit/?h=v5.4.2&id=cff39fba10ffc10ee4dcfdc66ff6528eb26462d3

Tested on: OS X 10.10.4, Windows 8.1 64 bits with both with QT 5.4.2 and 5.5.0