There is a following scenario that happens sometimes:
- Question is posted on math.SE.
- Question don't get any (useful) answers.
- Question is crossposted to Mathoverflow and is answered there.
Now, nothing bad have happened, definitely. But the original question still looks unanswered and it's not terribly convenient sometimes: it shows on "unanswered" tabs, sometimes it's bumped by community user (anything else?).
What should we do with such questions (if anything)?
One obvious thing is that posting a link in comments when question is x-posted would certainly be nice. (Maybe we should even explicitly require it in the FAQ — BTW, whatever conclusion we might arrive at, perhaps we should add something about x-posting to MO to the FAQ.)
(Hope, it's clear that I don't think such questions should be closed.)