[Pkg-postgresql-public] Bug#878032: postgresql: apt-get purge of 9.4 removed service for 9.6

[Allan Wind]

Package: postgresql
Version: 9.6+181
Severity: normal

Dear Maintainer,

I recently upgraded my server which pulled in 9.6.  Then I manually 
migrated the configuration and data and then I purged the old version 
with:

# apt-get purge postgresql-9.4  postgresql-client-9.4 postgresql-contrib-9.4 postgresql-doc-9.4

Surprisingly that also stopped my 9.6 instance and the service disappeared:
disappeared:

# systemctl |grep postgresql
  system-postgresql.slice                                                                                                        loaded    active active    system-postgresql.slice

To restore service, I did

# dpkg-reconfigure postgresql-9.6
# systemctl |grep postgresql
  postgresql.service                                                                                                             loaded    active exited    PostgreSQL RDBMS
  postgresql at 9.6-main.service                                                                                                    loaded    active running   PostgreSQL Cluster 9.6-main
  system-postgresql.slice                                                                                                        loaded    active active    system-postgresql.slice

To me this appears to be defective, and apologize if I missed an existing
report or if this should be filed against another package.

-- System Information:
Debian Release: 9.2
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 3.16.0-4-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages postgresql depends on:
ii  postgresql-9.6  9.6.4-0+deb9u1

postgresql recommends no packages.

Versions of packages postgresql suggests:
ii  postgresql-doc  9.6+181

-- no debconf information