QWebSocket emits bytesWritten twice

It seems bytesWritten signal in QtWebsocket connected twice :
from http://code.qt.io/cgit/qt/qtwebsockets.git/tree/src/websockets/qwebsocket_p.cpp?h=dev

line 576

{{ QObject::connect(pTcpSocket, &QAbstractSocket::bytesWritten, q, &QWebSocket::bytesWritten);}}

then in line 607 in same function.

also tested with echo client and verified the problem.