I do have the same issue on Centos 6.6, Plesk 12. My log file is 4gb and not rotated.
Rotation log is set by size 10240kb.
Access log is rotated well but error_log is not.
/var/www/vhosts/domain.tld/logs/error_log 4GB
/var/www/vhosts/domain.tld/logs/error_log.1 2GB...