Looks like I got an answer. I actually clicked on the ban link, and it claims I posted something 7 months back. Posted as "annon", which as a "name fag" is something I do not normally do. The link then points to an image I supposedly posted, giving instructions on joining a loli chat group, which I of course did not submit. So it would seem I was IP spoofed, and me clicking through to the message lifted the ban...

So... I believe a new level of security has been added? As the ban actually expired in March, and this seems to be something that triggered recently.