At least for Ubuntu users, I recommend filing those bugs on Launchpad. The package maintainers are usually able to tell pretty quickly if the issue is an upstream one, in which case you then file it upstream (in Gnome’s bugzilla) and link the two reports (there’s built-in functionality in LP precisely for this purpose). When the distributor’s tracker is your first port of call, you won’t (usually) be bothering upstream unnecessarily with distro-specific issues.

In fact, I sometimes file bugs on LP even when I know the issue is an upstream one, and then just link the reports right away. This way other Ubuntu users, who can’t tell the difference and would file the bug on Launchpad anyway, are saved the trouble.