Dart Language: MessageEvent.source not working properly on JavaScript

Question

I'm starting a listener on a MessageEvent, as follows:

window.onMessage.listen((MessageEvent e) {
    if (e.source == newWindow) {
        // Do something.
    }
});

And I'm opening "newWindow" like this:

newWindow = window.open("some_page.html", "");

Now let's get to the unexpected behavior:

 (e.source == newWindow)

Dart returns TRUE, while JavaScript (build from Dart Editor) returns FALSE.

Just to clarify, when "newWindow" sends a message to its opener (via window.opener.postMessage), my application should accept the message, since "source equals to newWindow". And it is, in fact, working. However just on Dart code. When the application is executed via JavaScript, this doesn't work. The verifying of "e.source equals to newWindow" returns false.

Any ideas on why this is happening?