It's sort of a bug, bug by design. It only shows topics from the last 200 or 250 posts, for speed reasons. This is usually more than enough to fill the spy. There were so many posts in "geekhack hacked again?" last night that this doesn't work at the moment and there are not enough unique topics in those 250 posts to fill the spy. It will fix itself. I might rewrite that code at some point.