Please see attached example of QNetworkReply::setReadBufferSize behavour.

I start this application from command line using some URL as a first parameter. I expect QNetworkReply::setReadBufferSize will limit buffer usage and I never see _reply->bytesAvailable() more than QNetworkReply::setReadBufferSize value (1048576 in this example).

It works excactly that way, when the example compiled with Qt4.7.4. When it compled with Qt4.8.0 or 4.8.1 I see some huge number instead which depends only on network bandwidth.