A question was recently asked that was a duplicate of another because the asker missed the original when searching. The duplicate was closed (and I think merged, since answers to the duplicate are now in the original, but I don't really know how merging works).
However, the original question is on the third page of active questions (because it's reasonably old). It seems like opening a duplicate question and/or merging a question should make it active in the same way that editing or answering it would.
(The closed question is still high in the active list, but people tend to ignore the closed questions).