QNetworkAccessManager stalled FTP requests after abort

#include <cassert>
#include <QCoreApplication>
#include <QUrl>
#include <QNetworkAccessManager>
#include <QNetworkReply>
#include <QNetworkRequest>
#include <QSignalSpy>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QNetworkAccessManager nam;
    QUrl url("ftp://mirror.netcologne.de/qtproject/archive/qt/5.7/5.7.1/md5sums.txt");
    QNetworkReply *reply = nam.get(QNetworkRequest(url));
    QSignalSpy spy(reply, SIGNAL(downloadProgress(qint64, qint64)));

    assert(spy.wait(5000));  // suceeds

    reply->abort();
    reply->deleteLater();

    reply = nam.get(QNetworkRequest(url)); // try again to the same host after abort.
    QSignalSpy spy_1(reply, SIGNAL(downloadProgress(qint64, qint64)));

    assert(spy_1.wait(5000));  // fails, any request to the same host stalls forever

    return 0;
}