No idea what I'm doing differently, but it works now. >_>
I know the cause. I had bookmarked lemmingsforums.com.
and the forum script works by analyzing referrers. The dot at the end of the domain, despite being perfectly valid, makes the referrer check fail.
Relying on referrers for basic functionality is bad site design in nearly any case. :> At least the usual case works here.
-- Simon