Hi TomGeo,
what makes you think, that there is any bug? There could be misconfigurations, operating system failures/issues, non-compatible packages and wrong or missing libraries and all these things might have nothing to do with Plesk. Due to the case that I administrate several Debian / Ubuntu - operated servers and all these servers have no issues that you described, I doubt, that this is a Plesk - bug.
The symlink at "
/usr/local/psa/var/log/maillog" normally links to the OS specific mail - log, located at "/var/log/*", but when you updated from Plesk 11.5 it might be the case, that it was not updated properly within any previous update/upgrade/patch. Please have a manual look at "
/var/log" and adjust the symlink manually to the one on YOUR system. Such misconfiguations can happen from time to time and are caused by unfinished updates/upgrades/patches. Normally such misconfiguation - issues are as well documented in the depending updates/upgrade/patch - logs at "/var/log/plesk-install" and/or "/var/log/plesk/install".
Plesk itself just making things easier for admins, but it does not replace an admin and his/her work.