ssmtp installation is broken: says debconf: DbDriver "config": /var/cache/debconf/config.dat is locked by another process: Resource temporarily unavailable

$ sudo dpkg --configure -a
$ echo Note that there was no output and so dpkg is not currently locked or broken

$ sudo apt install ssmtp
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed
  ssmtp
0 to upgrade, 1 to newly install, 0 to remove and 44 not to upgrade.
Need to get 0 B/42.5 kB of archives.
After this operation, 2,048 B of additional disk space will be used.
debconf: DbDriver "config": /var/cache/debconf/config.dat is locked by another process: Resource temporarily unavailable
Selecting previously unselected package ssmtp.
(Reading database ... 1861341 files and directories currently installed.)
Preparing to unpack .../ssmtp_2.64-8ubuntu1_amd64.deb ...
Unpacking ssmtp (2.64-8ubuntu1) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up ssmtp (2.64-8ubuntu1) ...
debconf: DbDriver "config": /var/cache/debconf/config.dat is locked by another process: Resource temporarily unavailable
dpkg: error processing package ssmtp (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 ssmtp
E: Sub-process /usr/bin/dpkg returned an error code (1)

$ echo ok so it seems to now be broken... is it deadlocked with itself or something?

$ sudo dpkg --configure -a
Setting up ssmtp (2.64-8ubuntu1) ...
debconf: DbDriver "config": /var/cache/debconf/config.dat is locked by another process: Resource temporarily unavailable
dpkg: error processing package ssmtp (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 ssmtp

$ echo yup dpkg is now broken

$ sudo apt remove --purge ssmtp
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED
  ssmtp*
0 to upgrade, 0 to newly install, 1 to remove and 44 not to upgrade.
1 not fully installed or removed.
After this operation, 2,048 B disk space will be freed.
Do you want to continue? [Y/n]
debconf: DbDriver "config": /var/cache/debconf/config.dat is locked by another process: Resource temporarily unavailable
(Reading database ... 1861359 files and directories currently installed.)
Removing ssmtp (2.64-8ubuntu1) ...
Purging configuration files for ssmtp (2.64-8ubuntu1) ...
debconf: DbDriver "config": /var/cache/debconf/config.dat is locked by another process: Resource temporarily unavailable
dpkg: error processing package ssmtp (--purge):
 subprocess installed post-removal script returned error exit status 1
Processing triggers for man-db (2.7.5-1) ...
Errors were encountered while processing:
 ssmtp
E: Sub-process /usr/bin/dpkg returned an error code (1)

$ sudo dpkg --configure -a
$ echo and now there are no errors again so this is clearly an ssmtp packaging bug or similar

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ssmtp (not installed)
ProcVersionSignature: Ubuntu 4.4.0-79.100-generic 4.4.67
Uname: Linux 4.4.0-79-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.6
Architecture: amd64
CurrentDesktop: GNOME
Date: Mon Jul 3 17:07:51 2017
InstallationDate: Installed on 2014-04-07 (1183 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
SourcePackage: ssmtp
UpgradeStatus: Upgraded to xenial on 2016-08-04 (333 days ago)