It's possible either something in the upgrade. I never actually ran the upgrade on our live site, but we ran similar code. Even so, it is possible it was something else we have been working on recently.
You had been one of the ones to get 2 copies installed magically, so I am a little concerned that anything else may have gone wrong. If you can verify your post table is doing well, that would certainly put my mind at ease.
Try checking via phpmyadmin. Look at non-wiki posts older than a month or so. For me, the pagetext field was NULL (which is why you noticed oddities in that other thread).