In my answer, I am pretty sure that the comment "@Arturo, I use AC without any guilt!" was written by me, yet now I see it incorporated into Robin's comment that immediately preceded it.
That's surely a bug?
I'm guessing that's not a bug per se, but human error from when Jeff said/did:
I'm going through and manually merging all the Robin Chapman comments on math.se, I want to record some of the comments responding to his comments as I do so (I delete these afterwards, since after the comments are merged, it's no longer relevant.)