WebSocket Sessions must be manually closed

Currently if a WebSocket session goes inactive due to the browser shutting down or the user closing a tab the browser does not send a close event to the server. This behavior seems the same with Chrome and IE.

The underlying TCP socket is however inactive and can be confirmed by calling a Session#isOpen which returns false. This will cause a build up of sessions unless the user does something like

 for (Session session : sessions) {
    if (!session.isOpen()) {
       session.close();
   }
}

This would need to be done periodically by the application. Shouldn't the server automatically close these sessions when the underlying socket goes inactive?