This was due to a concurrent access to the debconf database. This is usually a
very temporary and not reproducible situation. If you can reproduce it then use
the following command to find the culprit:
fuser -v /var/cache/debconf/config.dat
I'm closing this report but don't hesitate to reopen
** Attachment added: AptOrdering.txt
http://launchpadlibrarian.net/48449271/AptOrdering.txt
** Attachment added: Dependencies.txt
http://launchpadlibrarian.net/48449272/Dependencies.txt
** Attachment added: Df.txt
http://launchpadlibrarian.net/48449273/Df.txt
** Attachment added: