QNetworkRequestManager fails to complete post if read on the given QIODevice returns 0

When attempting to implement a bandwidth throttling for HTTP Post request using a sequential or non sequential QIODevice that has a modified readData function so that it only reads as much bytes as is allowed to keep the bandwidth quota, the Post operation stalls indefinitely (stops and never completes) if the function (readData) returns 0 (does not read anything).
According to comments in the QT code calling the function however it should be retried automatically, but apparently it is not.

In an other case, where a simple HTTP proxy is implemented, the same issue appears when the Incoming data are not fast enough so that readData has once or more return 0 the POST operation fails the same way as above.