Maybe the configuration of the Gentoo bugzilla could be modified to match a nice feature of the mozilla bugzilla. There in the advanced search form (see URL), resolved fixed is selected by default as well, so that you find dups and open issues. I would think that this could prevent some new dups.
I was unable to find the specific file in the bugzilla source that contains which are selected by default. If you could find the reference in the source, reopen this bug and paste it in, I would be more than happy to implement it.