Comment 3 for bug 401056

sysklogd fails on postrm during purge since it tries to delete the user syslog, but the replacement rsyslogd is logged in in as that user now.

D000002: fork/exec /var/lib/dpkg/info/sysklogd.postrm ( purge )
userdel: user syslog is currently logged in
/usr/sbin/deluser: `/usr/sbin/userdel syslog' returned error code 8. Exiting.
dpkg: error processing sysklogd (--purge):
subprocess installed post-removal script returned error exit status 1
Errors were encountered while processing:
sysklogd

maybe test for existence of rsyslog in post removal script?

if [ ! -f /etc/init.d/rsyslog ]
    then
        deluser --system --quiet syslog
fi

or suchlike