Update - I've tried it on Chromium and Epiphany (both Webkit) and Firefox on Windows and it happens on all of them. Could it be the remains of the old "Most recent posts" and "Most recent threads" sections? They're certainly active links to something. In most cases, all I could get was the user-profile, because the only visible part was the avatar, but on one occasion I managed to get a link to an actual post.
I think I'm seeing it because, since the latest upgrade, I've increased the font-size for the forum to make it legible. If I view it at "normal" size, the extra text is not visible, although there is an edge of an avatar showing, if I look hard enough.