Redirection loop for on domain and all of its subdomains

I have Secure Pages enabled on all of our sites that run stores (around 10 different sites) and it works for each subdomain for dev, testing, and production (dev., testing., www.) But for some reason it will not work on one of my other domains. Historically that domain hasn't needed the security, it was only displaying content, not processing transactions.

Now I need to add a subdomain and build a store for it and I'm finding that no matter what subdomain I use for that domain, it creates a redirection loop when you try to visit a non-https page. All https pages work fine and if I set the module so that it secures every page it works. But mixed protocol is breaking non secure pages with a redirection loop.

Since it's limited to just one of my domains I'm not convinced this is a problem with the module. The reason I'm asking for help here is in the hope that you can help me figure out just what is causing it.

The site settings between the trouble domain and all of the others are the same, I've cleared caches both in the db and in browsers, I've tried setting $base_url in settings.php to go between http and https, and I've checked my site's apache config file and the .htaccess file. I can find nothing obvious that would cause this redirect loop for this domain.

Any help would be greatly appreciated.