Replying to SimonKing:
I am very much sure that Jeroen said that this is the correct way to proceed: If one thinks that the ticket is a duplicate then you review it accordingly, putting it as "positive review". Then the RELEASE MANAGER (nobody else!!) closes the ticket by choosing the resolution "duplicate", if he believes that the reasons given in the review make sense.
True, but you forget one important step: you should put the milestone to sage-duplicate/invalid/wontfix yourself, so I know the intention is to close this ticket as duplicate and no patch should be merged.
Nobody except for the release manager should close or reopen tickets (with a few exceptions like spam tickets, tickets marked as duplicate by the person who reported the ticket and with no other activity).
And if it's a duplicate, it would be nice to add a pointer in the description to the ticket of which it is a duplicate of.