Okay, first of all it's a common misconception that you are on a particular proxy, you aren't. ntl's proxy servers work as a group - so if your default group is Belfast then you will get routed to a different proxy server (from belf 1 to belf 5) depending on the IP of the target site - this is how they load balance.
Secondly, if you have tested all five (and they work) then it makes no sense that it would then fail if you allow ntl to choose, since you will still get one of the same five servers, with the same result.
Out of curiosity, I'll try them myself.
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Belfast 3 is still returning the old page.