Comment 3 for bug 53868

$ ps aux | grep update
65:bjourne 4441 0.1 2.0 18904 10336 ? Ss 02:27 0:00 update-notifier
79:bjourne 4538 0.0 0.1 2888 820 pts/0 S+ 02:30 0:00 grep --color=auto -n update
$ killall update-notifier; update-notifier
(Nothing is printed)

More from terminal:
$ sudo apt-get update
....
$ sudo apt-get upgrade
...
Följande paket kommer att uppgraderas:
  language-pack-en language-pack-gnome-en language-pack-gnome-sv language-pack-sv xinit
...

So there definitely is updates, but update-notifier fails to indicate that.