This was fixed in update-notifier 0.119ubuntu5. Changelog:
update-notifier (0.119ubuntu5) precise; urgency=low
* Make sure /usr/lib/update-notifier/package-data-downloader is called on package configuration as well, since a trigger is not guaranteed to happen if the triggering package is configured first. LP: #977178.
This was fixed in update-notifier 0.119ubuntu5. Changelog:
update-notifier (0.119ubuntu5) precise; urgency=low
* Make sure /usr/lib/ update- notifier/ package- data-downloader is called on
package configuration as well, since a trigger is not guaranteed to
happen if the triggering package is configured first. LP: #977178.