It seems this wasn't a bug in update-notifier, but a problem with the download server. From what I see in the logs, update-notifier was working as designed.
** Changed in: update-notifier (Ubuntu) Status: Confirmed => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/994125 Title: unable to install ttf-mscorefonts-installer To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/update-notifier/+bug/994125/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs