The following features were added:

[+] (Windows) BIND DNS server was updated to version 9.9.4-P1, CVE-2013-6230 vulnerability is closed.
[+] (Windows) Horde webmail was updated to version 5.1.5, CVE-2013-6275 vulnerability is closed.

The following functionality was improved:
[*] Plesk will remove the skip-bdb option from my.cnf if MySQL version is 5.1 or later. (PPPM-981)

The following issues were resolved:

[-] The piped logging feature did not write access_logs for add-on domains and subdomains.
[-] Plesk could not register PHP handlers because of wrong directives in php.ini or if running php -v returned exit code 1. (PPPM-808, PPPM-885)
[-] Chained SSL certificates no longer worked with nginx after upgrade.
[-] During upgrade to Plesk 11.5, the directories of add-on domains were incorrectly relocated in the new structure of virtual hosts.