Apparently, updating to the latest WP release did not help.
I’ve also been having this “problem” for the last couple of days (my last post on 2.2 mysteriously showed up as “Comments off”). After reading the WP site about the security flaws and fixes in 2.3.3 I decided to upgrade, and then posted about it on my blog. Today, I found the “Comments off” on my most recent post AGAIN.
Taking a closer look at both of the affected posts, I found something VERY interesting. Both were edited and a large amount of spam (links) was appended to the end of the post.
I suggest you go to your dashboard and edit your posts to see if you had your posts modified as well. I think it’s quite likely another WP vulnerability that hasn’t been found by the devs yet (or not fixed yet).
At the moment, I’m just removing the spam links from my posts. It appears that only the MOST recent post can be modified, but I haven’t gone through all of my posts yet so I’m not 100% certain.