PSA has finally issued a fix for this, as well as a hotfix.
The hotfix allows to pass environment variable PHP_SAFEMODE_SUPPORT in output for script assigned to event handler in Parallels Plesk Panel.
The hotfix is in the attachment. To instal the hotfix move the archive to Plesk root directory and extract it:
~# cp psa_patch_134765.tar.gz $PRODUCT_ROOT_D ~# cd $PRODUCT_ROOT_D ~# tar -zxvf psa_patch_134765.tar.gz
Where $PRODUCT_ROOT_D is /usr/local/psa for RedHat-like operating systems and /opt/psa for Debian and Ubuntu.