Non-fatal error received during ssl websocket connection over HTTP proxy

#include <QtWebSockets/QWebSocket>
#include <QObject>
#include <QCoreApplication>

class tst_QWebSocket : public QObject
{
    Q_OBJECT

public:
    tst_QWebSocket();
    ~tst_QWebSocket() {;}

public slots:
    void onConnected();
    void onReceivedText(const QString &aMessage);
    void onDisconnected();
    void onWsConnectionError(QAbstractSocket::SocketError aError);
    void onWsSslErrors(const QList<QSslError> &aErrors);

private:
    QWebSocket mWebSocket;
};

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    tst_QWebSocket tstSocket;

    return a.exec();
}

tst_QWebSocket::tst_QWebSocket():
    QObject()
{
    mWebSocket.open(QUrl(QStringLiteral("wss://echo.websocket.org")));
    connect(&mWebSocket, SIGNAL(connected()), this, SLOT(onConnected()));
    connect(&mWebSocket, SIGNAL(disconnected()), this, SLOT(onDisconnected()));
    connect(&mWebSocket, SIGNAL(textMessageReceived(QString)), this, SLOT(onReceivedText(QString)));
    connect(&mWebSocket, SIGNAL(sslErrors(const QList<QSslError> &)), this, SLOT(onWsSslErrors(const QList<QSslError> &)));
}

void tst_QWebSocket::onConnected()
{
    qDebug() << "Connected";

    mWebSocket.sendTextMessage("TestHello!");
}

void tst_QWebSocket::onReceivedText(const QString &aMessage)
{
    qDebug() << "Got echo: " << aMessage;

    mWebSocket.close();
}

void tst_QWebSocket::onDisconnected()
{
    qDebug() << "Disconnected";

    qApp->quit();
}

void tst_QWebSocket::onWsConnectionError(QAbstractSocket::SocketError aError)
{
    Q_UNUSED(aError);

    qDebug() << "Websocket connection error: " << mWebSocket.errorString();
}

void tst_QWebSocket::onWsSslErrors(const QList<QSslError> &aErrors)
{
    foreach (const QSslError &error, aErrors)
    {
        qDebug() << "Websocket SSL handshake error: " << error.errorString();
    }
}

#include "main.moc"

$ http_proxy=http://192.168.85.153:3128 ./WebSocketProxyTest
Connected
Got echo:  "TestHello!"
QIODevice::write (QTcpSocket): device not open
Disconnected