Comment 5 for bug 975878

The postinst is not incomplete; the downloading has been moved out of the maintainer script so that download failures don't cause cascading package installation failures.

Please attach /var/log/apt/term.log from the affected system, and show the output of the following commands:
ls -l /var/lib/update-notifier/user.d/
ls -l /var/lib/update-notifier/package-data-downloads/