CasperJS File Download Times Out After 30 Seconds

I'm using CasperJS to download a 15 MB file. In the browser, the download takes about 3 minutes to complete. With Casper, the .download function for the same url returns after exactly 30 seconds, and the file written to disk is 0 bytes. I've tried setting longer timeouts like this:

var casper = require("casper").create({
    pageSettings: {
        webSecurityEnabled: false
    },
    waitTimeout: 500000,
    stepTimeout: 500000
});

But they have no effect. Here's my download function:

casper.on('resource.received', function (resource) {
    var url, file;
    if ((resource.url.indexOf("myDownloadUniqueString=") !== -1) ) {
        this.echo(resource.url);  // the echo'ed url can be downloaded in a web browser
        url = resource.url;
        file = "downloaded_file.wav";  // this will be 0 bytes
        try {
            var fs = require("fs"); // phantom js file system (not node)
            casper.download(resource.url, file);
        } catch (e) {
            this.echo(e);  // no error is thrown
        }
    }
});

Any ideas? Perhaps an issue with the PhantomJS fs methods, but that documentation is incomplete...