We don't document such internal aspects.
Anyway, the Server issues that log line when it detects a connection interruption. Hence, from the Server point of view, the client has detached first and there is no way (and no point) for sending a notification.

I don't understand why the user action causes the connection to be interrupted but the page not to be reloaded. What exactly is done by your code when the user returns to the browser after a long while? Can you confirm that the PushPage object is still active? In such a case, the client application should receive a onStatusChange() or onEngineLost() notification.