Yes, it is a problem that people occasionally have with proxy servers - you and Phil both share the same ISP, and they force you to use a proxy server. Their proxy server is most likely MS Proxy, which is not completely compliant with the HTTP specifications, and as such there are occasionally problems.
This is the first time I have heard of anyone having access to someone else's actual setting though - usually it just looks like you are logged in as someone else, but you are actually really logged in as yourself.
I will be implementing some changes today which should hopefully avoid these problems in future.