I think I've given sufficient detail to re-create the issue so it warrants further investigation. Waiting for someone else to hit the same problem and find this might mean it never gets confirmed otherwise.
** Changed in: coreutils (Ubuntu) Status: Unconfirmed => Confirmed -- sort's -u is Failing to Check all -k fields for Uniqueness. https://launchpad.net/bugs/56891 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs