Comment 7 for bug 1105137

I was able to recreate and research this a bit during an upgrade from Q to R. I received the debconf prompt regarding rsync, cups, cron and atd. The preinst script for libc checks to see whether or not $RELEASE_UPGRADE_MODE = desktop. This evironmental variable is set by ubuntu-release-upgrader in DistUpgradeController. Additionally, the result of this check is logged in /var/log/dist-upgrade/main.log as "run in 'desktop' mode" or "running in server mode".

Inspecting the running process at the time of the distribution upgrade I found RELEASE_UPGRADE_MODE set to desktop for a dpkg process, a perl / debconf process, and a dpkg preinst. Its not quite clear where the problem lies but it doesn't look like it is an issue with ubuntu-release-upgrader.