I've done some more digging around, and it now looks more likely that the culprit is the mappings in the file:
/usr/share/X11/locale/el_GR.UTF-8/Compose which belong to the package "libx11-data". ** Package changed: gtk+3.0 (Ubuntu) => ubuntu ** Package changed: ubuntu => libx11 (Ubuntu) -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1025291 Title: Compose key yields incorrectly accented Greek characters when using Greek keymap To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/libx11/+bug/1025291/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs