UDP Socket cannot send via (unbind) port.

The broadcast sender example is not able to send via the (unbind) socket.

This is the original code:
QByteArray datagram = "Broadcast message " + QByteArray::number(messageNo);
udpSocket->writeDatagram(datagram.data(), datagram.size(),
QHostAddress::Broadcast, 45454);

To show the problem, I changed the source like this:
QByteArray datagram = "Broadcast message " + QByteArray::number(messageNo);
if(1 == udpSocket>writeDatagram(datagram.data(), datagram.size(), QHostAddress::Broadcast, 45454))
qDebug() << "error on write datagram";

This Variant is working:
if(!udpSocket->bind(QHostAddress::AnyIPv4, 12345))
qDebug() << "error on bind";

QByteArray datagram = "Broadcast message " + QByteArray::number(messageNo);
if(1 == udpSocket>writeDatagram(datagram.data(), datagram.size(), QHostAddress::Broadcast, 45454))
qDebug() << "error on write datagram";

To make the example working, the port to bind to is unimportant.