Why doesn't Zombie.js work with Google Charts?

I have a simple web page that loads the Google Chart API:

<script type="text/javascript" src="https://www.gstatic.com/charts/loader.js"></script>
<script type="text/javascript">
    google.charts.load("current", {packages:["corechart"]});
    console.log("load() called");
</script>

It works fine when I hit it with my browser. In Chrome, the load() call requests a bunch of external resources:

In Zombie, only one external resource is requested:

zombie Opened window http://localhost/graph  +7s
zombie GET http://localhost/graph => 200 +17ms
zombie Loaded document http://localhost/graph +15ms
zombie GET https://www.gstatic.com/charts/loader.js => 200 +71ms
load() called
zombie Event loop is empty +135ms

Here is my simple Zombie code, for reference:

Browser.visit('http://localhost/graph', function (err, browser) {
    if (browser.errors.length > 0)
        return console.log(browser.statusCode, browser.errors);
});

No errors are reported. I have also tried waiting for several seconds, browser.wait(), as well as a full web page that actually loads a chart. Zombie never loads the other resources and, naturally, never calls any of the Google Charts callbacks.

Why does Zombie seem to be unable to use the Google Charts API?

via ladenedge