Dropped network requests on Windows Phone

There are some major issues with networking on Windows Phone, reproducible in a number of scenarios. In my case replies from XMLHttpRequests are randomly dropped. I can also reproduce this using Image elements in QML as well as with QNetworkAccessManager directly. In many cases I will simply not get a response from a request, not even an error. It seems I can work around this issue by creating a separate QNetworkAccessManager per request, which is obviously not optimal.