Well, since we're all playing Cluedo, My take:
The class C ban was already in effect for a long time. Certainly there was some mention of it when a certain member (like you can't tell who) was permanently banned some time back.
Some time later, but before the hosting upgrade (I think) a Sky ISP user on aw.net (Amigaone Productions, IIRC) reported being blocked. I wasn't able to sort it out as the built-in IP ban tools are not available to moderators and suggested he use a proxy. I can't find that thread right now, but if I do, I'll post a link.
It seems that nobody really made a big deal out of it since then. I believe the issue kicked off again due to comments made on this thread...
http://amigaworld.net/modules/newbb/viewtopic.php?topic_id=34172&forum=2... particularly Steve's comment here:
Well, it would have to be AWN for me. I used to visit others (I still go to EAB), but A.O with it's lovely ban on my ISP has rendered my visits to the site impossible
It was my understanding that whatever restrictions had been put in place to keep the aforementioned member banned were overturned in their entirety when he was permitted to return. I'd have to do some IP address checks, but it could just be that he was using a proxy once his ban was lifted and the IP address range ban was never revoked. More likely, it was probably just forgotten about - certainly the admin seemed unaware.
I don't see any evidence to suggest that someone has broken in and added this IP ban recently.