I just noticed, using IE 6.0 (sp2), if I view a page that has categories, but not many, when the browser stops writing the categories or discussions, the links on the left stop working as well.
This is hard to explain so I included a screenshot.
I can confirm this bug. (IE 6.0 SP2; Windows XP Home SP2.) It's pretty easy to replicate. Just look at the Stickies or Testing categories. No idea what's causing it, though.
I get slightly different behavior--looking at a thread there is nothing visible below your line--until I hover over the 'bookmark this discussion' link, then the entire panel appears. When hovering over any of the tabs at the top, the bottom half of the panel disappears again.
Sure, I don't have a login over there, I found vanilla after the March 25th when you moved the user/pass database over... I'll submit a request for a login. :)