I've had a couple of people ask me about lost comments recently - there have been cases where a comment went in, and then disappeared. I thought about that while I was driving yesterday, and I figured out that yes, it was a possibility if two or more people commented in rapid succession. So, I've been working on a fix this morning - and I'm testing it against my local (test) server. When I'm convinced that I didn't add a new bug, I'll upload the fix.
Update: the fix is uploaded.