Comment 5 for bug 1396787

After digging a bit deeper I found out that that the default configuration of /etc/apt/apt.conf.d/50unattended-upgrades is exactly the same as I had in my experiment i.e.
- the ${distro_id}:${distro_codename}-security origin is ENABLED
- the ${distro_id}:${distro_codename}-updates and others origin are DISABLED

The consequences are the following. A fresh install of Ubuntu LTS e.g. 16.04 keeps installing the *-security updates, but not the *-updates ones. The number of packages with new versions in *-updates repository keeps growing unless somebody installs them manually. It is a couple of clicks, but still many people never do it. As the list of upgradable packages grows, unattended-upgrades get slower and slower to the point that it may take hours to complete. Effectively, the automatic updates may no longer work at all depending on how a given system is used. Also the user experience gets worse with CPU busy executing the unattended-upgrades script.

All in all, I consider it a serious issue that requires attention.