Comment 13 for bug 549217

There doesn't seem anything special to be necessary to reproduce.

Maybe it's the usage pattern. The computers are usually not running for more then 2-3 hours at at time, then shut down until next boot.

Konstantin does not get any out of the box notifications of security updates.
Original reporter's and my reports have auto installation of security updates enabled, and those don't work either.

In both cases running update-manger manually (after some time that brought new security updates passed) shows a list with security update that have accumulated, but they did not properly trigger automatic notification/installation.