Comment 6 for bug 996851

In case of gedit this is mostly true, as there are only minor changes added by Ubuntu to gedit, so most of the times functional problems should be reported to GNOME. Theming/styling issues can be caused by the Ubuntu default theme, so those ones you should not report to GNOME, but rather to ubuntu first, and a bug triager will decide whether it's an upstream issue or an ubuntu issue. However please keep in mind that this is only true for gedit, as other applications might have a large set of ubuntu-specific changes (e.g. System Settings aka gnome-control-center), so the problem you are experiencing with them might be only ubuntu-specific.

However it's always good to have the bugs reported in ubuntu if you have found the bug in ubuntu, and upstreaming should follow only after the bug has been reported to ubuntu.

I hope this helps, if you have any other questions, I will try to answer them.