QTcpSocket disconnected not emitted

//test.h
#include <QTcpSocket>

class Test : public QObject
{
Q_OBJECT
public:
Test();
public slots:
void Connect();
void Disconnected();
void Connected();
void Error(QAbstractSocket::SocketError e);
void ChangeState(QAbstractSocket::SocketState state);
void readyread();
protected:
QTcpSocket _socket;
};

#include "Test.h"
#include <unistd.h>
#include <iostream>

Test::Test()
{
connect(&_socket, SIGNAL(connected()), this, SLOT(Connected()));
connect(&_socket, SIGNAL(readyRead()), this, SLOT(readyread()));
connect(&_socket, SIGNAL(disconnected()), this, SLOT(Disconnected()));
connect(&_socket, SIGNAL(error(QAbstractSocket::SocketError)), this, SLOT(Error(QAbstractSocket::SocketError)));
connect(&_socket, SIGNAL(stateChanged(QAbstractSocket::SocketState)), this, SLOT(ChangeState(QAbstractSocket::SocketState)));
}

void Test::Connect()
{
std::cout << __FUNCTION__ << std::endl;
_socket.connectToHost("127.0.0.1", 5001);
if (!_socket.waitForConnected(1000))
{
return;
}
}

void Test::readyread()
{
std::cout << "readyread" << std::endl;
}
void Test::Disconnected()
{
std::cout << "disconnected" << std::endl;
}

void Test::Connected()
{
std::cout << "connected to " << std::endl;
}

void Test::Error(QAbstractSocket::SocketError e)
{
std::cout << __FUNCTION__ << std::endl;
}

void Test::ChangeState(QAbstractSocket::SocketState state)
{
std::cout << state << std::endl;
}

int main()
{
Test t;
t.Connect();
while (1)
{
sleep(1);
}
}


when i closed the server, Disconnected was not called.