QTcpSocket and proxy server configured in windows

I am using Qt 5.8 and windows 7 OS.

I have written below code which is working fine when proxy server in windows is not configured. If we configured proxy server with "IP address" and "port" then below code is not working and it gives "Operation not permitted" on Qt creator application output when we bind the socket.

QTcpSocket socket;
quint16 port = 0L;
socket.bind(0, QTcpSocket::ShareAddress);
port = socket.localPort();

When we configured proxy server in windows through "LAN Settings" then it is giving "0" as port number and we not configured proxy server then it gives correct random port number.

Can you please suggest what is wrong ? Is this known issue ?