I am starting to see this very often and find it very annoying: people report a bug, later they find a preexisting report for the same bug, they then mark that preexisting bug as a duplicate of their bug. I end up getting lots of "this bug has been marked as a duplicate of bug x" emails and this is VERY annoying. To prevent this people need to rigorously check for a preexisting report. Second, when you find two duplicate bugs, search the bug tracker for any more duplicates and mark all of the newest duplicates as duplicates of the oldest bug. This prevents chains of duplicates which in turn maximizes the efficiency of the bug reporting and fixing process.
report 1 -> report 2 -> report 3 -> report 4 | | | | Commenters Commenters Commenters All commenters from report 1 from reports 1-2 from report 1-3
report 1 ----\ commenters 1 \ report 2 ------> report 4 commenters 2 / all commenters report 3 ----/ commenters 3
In the chained version commenters move from report to report wasting comments on bugs that will probably never be seen again after being marked a duplicate. In the non-chained version commenters move directly from the duplicate to the final (and oldest) bug report wasting as few as comments possible on the duplicates.