memory usage when downloading large files on iOS with https

When downloading a large file on iOS via QNetworkReply using https,
the whole file seems to be held in memory during download.
After the download is complete, the memory usage is back to normal again.
this is no problem unless you want to download really large files (200MB)
and iOS can't allocate more memory and crashes.
The same download with a normal http request doesn't show this behaviour.

I think the reason is that in qtbase/src/network/access/qnetworkreplynsurlconnectionimpl.mm
in didReceiveData the data is always appended to the responseData variable,
but in readData the read data is not removed from responseData.