db_purge does not purge

Binary package hint: debconf

I find that db_purge of debconf does not purge when i purge and reinstall krb5-config package with apt-get.

Steps to reproduce:
- Check retrieval info of "dnsdomainname" and must return some domain
- install krb5-config package and check "default_realm" in /etc/krb5.conf
- purge krb5-config package
- Change and check the domain name of the machine
- install krb5-config again

In the second install of krb5-config the default_realm still equal the first domain-name because when the config script get "krb5-config/default_realm" with db_get remains the previous configuration

PD: excuse my English is not my strength

ProblemType: Bug
Architecture: amd64
DistroRelease: Ubuntu 9.04
Package: debconf 1.5.26ubuntu3
PackageArchitecture: all
ProcEnviron:
 LANG=es_AR.UTF-8
 SHELL=/bin/bash
SourcePackage: debconf
Uname: Linux 2.6.28-15-generic x86_64