A couple of times (that I know about), people have asked a question on Travel:SE; been told that it is really on topic here; duplicated the question here; ... and then the original question has been migrated from Travel:SE.
One way to handle this is to close one of the questions as a duplicate of the other. However this isn't as helpful as it might be because usually one question is a copy-and-paste duplicate of the other (so retaining both does nothing for adding diversity to search terms).
Can we have a way of merging a migrated question with a pre-existing exact duplicate?