It should return you the front page html. It may also return you an error.
If you are landing on the centurylink search page off of those sites I would be willing to bet they somehow messed up the DNS resolver and Proxy server at the same time.
You can also do something like 'GET /blahblahblah.txt' and see if you get an error back. That may give you some more information about what is going on.
Also I remember awhile back someone talking on another site about how you can sometimes have configuration tools to set this sort of thing. You log into the site and they give you a way to set what is screened out.