Nick,
Very glad to hear you found the issue! I wouldn't have ever found that, and likely would have thought you were crazy when I tested remotely since that setting wouldn't matter. As for jQuery, we load a local copy of it (from your server), so it should seem local. The only reason IE should detect it as remote and not load it is if you're disabling the SCLogin's jQuery inclusion and relying on a template or other extension to load it *and* that other inclusion is trying to load a CDN version, like from Google APIs or something.
Either way, glad it's going for you, and let us know if there's anything else we can help with!
Thanks,
Alex