Using CasperJs + SlimerJS for testing 3rd party tracking. Calls don't go out

Question

I have been using CasperJS + PhantomJS to walk through a site, http://example.com. As it does so, tracking calls to http://just_another_tracking_service.com/?with&some&params are fired (I have a separate scripts that captures and deals with those calls). These always return a tiny gif, with the correct mime type. The protocol for the gifs is http.

I have been trying to use the same CasperJS script to do the same with SlimerJS - the walking-though-the-site part works very well (much better than PhantomJS in fact). But no calls to http://just_another_tracking_service.com/ are sent. I have tried enabling web security this way, but no joy.

Edit: removed pageSettings from code sample, it didn't make any difference, as this page explained http://docs.slimerjs.org/current/configuration.html

var casper = require("casper")
             .create({ waitTimeout: 10000 });

Any ideas what I am doing wrong / what should I be doing? Thanks in advance.