I dealt with this a lot at a hosting company I worked for. This is almost certainly a .htaccess file that is set to only redirect based on referrer. It is normally under several hundred blank lines, to make it look empty to the casual observer.
I can't access the linked url (it's https: http://news.ycombinator.com/item?id=3575029), but as far as I remember, if an HTTPS page links to (or redirects to) another page that is not on the same domain, the HTTP REFERRER field will be empty.
