From: "Lloyd Palfrey" <Lloyd at wsufftrust dot org dot uk>

> I've added 00:12:17:a9:9c:80 to the MAC address filter on the access
> points. This seems to have solved the problem. However there must be a
> bug somewhere... How else could 00:12:17:a9:9c:80 authenticate to the
> CP.

Captive portal is IP based, noy MAC based.  He is just riding on someone 
elses authenticated IP.

                                Lee