The main idea:
suppose we make two request into the
QNetworkReplay* QNetworkAccessManager::get()
with the same host name.
This method return QNetworkReplay* object where we can “subscribe” to signals for tracking the replay status. For example it can be “error()” signal.

We make the two get() request with the wrong host address ….
AND! If we make one request with the same host (it’s important!) and then make second request before the host from first request will be processed, we are never receive the notification (about error) from the second request, because the host look up for the second request are not performed (the variable QHttpNetworkConnectionPrivate::networkLayerState in InProgress state) and host look up also async operation.

I record the video for explain this problem.

If it need I can submit my patch for fix this bug.

p.s.
Link to my post on qt-project.org forum: http://qt-project.org/forums/viewthread/31107/