There is your answer. Whatever it picks up is not the same setup every time. Some connection may have strong firewalls and other no firewall.

I really don't see the meaning in adding 127.0.0.1 or anything unless it was a networked firewall. And then it would still be better to have the exact IP for your PC. But in your case it probably changes a lot. That's the price you have to pay for leeching someone elses connection. I don't suppose getting your own is an option