Plesk 12.x / Linux :: Spamassassin Installation Error - Ubuntu 14.04

Installing Plesk Panel with Spamassassin on Ubuntu 14.04 LTS gives a significant error:

Restarting SpamAssassin Mail Filter Daemon: No /usr/bin/perl found running; none killed.
server socket setup failed, retry 1: spamd: could not create IO::Socket::INET6 socket on [::1]:783: Cannot assign requested address
server socket setup failed, retry 2: spamd: could not create IO::Socket::INET6 socket on [127.0.0.1]:783: Address already in use

server socket setup failed, retry 9: spamd: could not create IO::Socket::INET6 socket on [127.0.0.1]:783: Address already in use
spamd: could not create IO::Socket::INET6 socket on [127.0.0.1]:783: Address already in use
invoke-rc.d: initscript spamassassin, action "restart" failed.
dpkg: error processing package sa-compile (--configure):

even though spamassassin (i.e. spamd) is not running. The usual suspects for the before mentioned error, being

a) differences in the name of the PIDFILE variable in /etc/default/spamassassin and /etc/init.d/spamassassin
b) directory and/or file location are not readable/writable

are not causing this specific installation bug. The work-arounds:

1 - not installing spamassassin (not an option)
2 - installing spamassassin and (afterwards)

change /etc/default/spamassassin, add the option "-4" to the line OPTIONS, resulting in the line: OPTIONS="--nouser-config -4 --username=popuser --daemonize --helper-home-dir=/var/qmail --virtual-config-dir=/var/qmail/mailnames/%d/%l/.spamassassin --create-prefs --max-children=5"
run plesk-installer or autoinstaller again ..Work-around 2 works fine, after reinstallation the /etc/default/spamassassin is as it should be (note that the added "-4" is not present anymore).

The before mentioned work-around suggests some error in the installation process, very likely to be an issue with the chronological order of installation of the various components. In theory, it can be excluded that this bug/issue is caused by psa-spamassassin and/or spamassassin (version 3.3.x) packages, even though some current spamassassin bugs are known: URL....I sincerely hope that Parallels Team can investigate and patch both of the bugs/issues.