This question was asked by Kit, an answer was given by Willie Wong a short time later, and immediately after that, Willie Wong added a comment to his answer. That's all the activity I see on this question. Nevertheless, on the list of active questions it says (right now) that the question was modified by Geoffrey Jones 16 hours ago. How can this happen? (I think I saw this strange behaviour before, but I don't remember the question.)
EDIT:
Jukka's answer made me understand this. So it's not really a bug, but probably by design. Somehow I would like it if the software would not only remove the answer but also the recent edit marker. The only benefit of leaving the "recent edit by Geoffrey Jones" in the above example is for those few who saw the answer and then saw it disappear. This benefit is rather temporary ...