Hosted Tokenization firing "message" on initial load of iframe?

Hi.

It seems that the hosted field tokenization is triggering a "message" on first loading the iframe. We have an iFrame and it is targeted to Moneris for the hosted field like so (the profile Id is one from the QA environment, not ours ;) ).

<iframe id="monerisFrame" src="esqa.moneris.com/.../index.php class="form-control"></iframe>

 And we register a message handler like so (have also used the listener code as shown in the Moneris documentation for Hosted Tokenization)

window.onload = function() {
    $(window).on("message", function(e) {debugger;});
};

 Upon loading the page with that code, it immediately breaks at the `debugger` statement and when I browse the information on `e` it shows that the originalEvent.origin is `https://esqa.moneris.com`. However, we have not posted a message to trigger that. I've attached an image showing the info on the event object received.

The above applies to the Moneris QA environment, not sure about production at this time.

Thank,

Mark