Comment 6 for bug 325160

With all due respect to Pedro & Sebastien, I think that Giuseppe is right here.
Until now, it has been standard procedure to mark duplicate bugs as duplicate, with a link to the master bug and a comment giving this standard response:
https://wiki.ubuntu.com/Bugs/Responses#A%20duplicate

I am not very comfortable with this new trend, to just close as invalid. Not all users know what is a duplicate bug and how to search for it (let alone reliably find it). It is our job to find the duplicates for them and to help them follow the bug resolution process (upstream reporting, in progress, fix committed and released).

As a personal opinion, I think it's better to leave the bug open (as New) until we have the time to actually find the duplicate, than to mark as invalid and leave the bug reporter in the dark...