Plesk 12.5 PHP-FPM via Nginx switch PHP version fails 1st attempt

[TimReeves]

Specifically (tried on 3 Ubuntu servers, 12.04 and 14.04) I was trying to move up from PHP 5.6.16 FPM via Nginx to PHP 7.0.0 FPM via Nginx. A message like this appears:

Error: phpinimng failed: invoke-rc.d: initscript plesk-php56-fpm, action "status" failed. invoke-rc.d: initscript plesk-php56-fpm, action "status" failed. Service plesk-php56-fpm is down after attempt to start it

The message is plain wrong. What has happened is:

• The fpm pool config has been removed from /opt/plesk/php/5.6/etc/php-fpm.d
• BUT PHP 5.6 FPM is still running including for the site in question (i.e. it was never stopped)
• "service plesk-php56-fpm restart" works - the website in question then has no PHP service
• Manually create an appropriate pool config in /opt/plesk/php/7.0/etc/php-fpm.d
  
• service plesk-php70-fpm restart

Now the domain in question is serviced by PHP 7.

Subsequent reassignments in Plesk to the new PHP version work without problem, so the problem only exists when the target FPM pool is empty.