Hi
I do not have good news. Programmers was not able to figure out why it's not working either, but they've made an ultimate test and made a copy of Your site and installed it on other server. Saving work without a problem than. This means it's not an issue with code in files, but must be something from outside. Most likely some server feature/configuration option. Please show this to Your hosting provider, maybe they know some of serve function capable of such redirection.