. I do have my preference set so the most recent post is at the top, and when I'm not logged in it's the opposite way around. ...still, I could almost swear that this time reversal happened when I was logged in. One thread went in the correct direction, the next thread went in the other direction, and the thread after that was back to normal.
...I can't seem to reproduce the error now, so if nobody else has experienced this maybe we should just assume that it was the logged-in/logged-out issue.