error: Cannot find a question for

I am still trying to write autoinstallation manifests for puppet, which should install several packages, including sympa.

Unfortunately, the sympa postinst script is overengineered and cannot be run in a non-interactive mode without giving answers through preseed.

I therefore tried to add configuration value through the debconf mechanism, which permanently fails once the sympa package had been installed (and removed again with --purge). I've tracked the problem down to

echo "sympa\tsympa/dbconfig-install\tboolean\tfalse" | debconf-set-selections -v
info: Trying to set 'sympa/dbconfig-install' [boolean] to 'false'
info: Loading answer for 'sympa/dbconfig-install'
error: Cannot find a question for sympa/dbconfig-install

This works on a clean, fresh system where sympa had never been installed, but once it was installed, debconf-set-selections fails.

/var/cache/debconf/templates.dat contains

Name: sympa/dbconfig-install
Description: Dummy template
Extended_description: This is a fake template used to pre-seed the debconf database. If you are seeing this, something is probably wrong.
Type: boolean
Owners: sympa/dbconfig-install

So it seems as if the templates.dat gets somewhat broken.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: debconf 1.5.51ubuntu2
ProcVersionSignature: Ubuntu 3.13.0-19.40-generic 3.13.6
Uname: Linux 3.13.0-19-generic x86_64
ApportVersion: 2.13.3-0ubuntu1
Architecture: amd64
Date: Thu Apr 3 23:36:26 2014
PackageArchitecture: all
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/usr/bin/tcsh
SourcePackage: debconf
UpgradeStatus: No upgrade log present (probably fresh install)