PHP script can't communicate with unzip/gzip

[AlterTag]

Hello to advanced users and Plesk Support !
I'm asking a help.

I have Plesk 10.4.4 Update #25 on Linux CentOS 2.6.32-220.7.1.el6.x86_64, dedicated server, root shell access available.
PHP is set to use FastCGI.
PHP settings for customers disabled to use only main /etc/php.ini
Safe mode OFF.
All other settings are default, fresh installation made.
Physically unzip and gzip binaries are available in /usr/bin

Problem description
I have a simple PHP script I've used before on many shared hostings without a problem.
But now after installation it does not see (and, accordingly, does not perform) UNZIP and GZIP operations.
All other functions of the script work properly.
Installation path /var/www/vhosts/MYDOMAIN.com/httpdocs/

PHP script CONFIG file contains the following configuration for unzip/ungzip
$config_automationHandler = "php";

$config_automationUnzipPrograms = array();
$config_automationUnzipPrograms["unzip"] = "/usr/bin/unzip";
$config_automationUnzipPrograms["gzip"] = "/usr/bin/gzip";

(Also tested with same negative result)
$config_automationUnzipPrograms["unzip"] = "/usr/bin/unzip";
$config_automationUnzipPrograms["gzip"] = "/usr/bin/gunzip";

******
But PHP script Support Info shows that
Automation Handlers
php Available
curl Available
Automation Unzip Programs
unzip Not Available
gzip Not Available
**********

So, it can't unzip (or ungzip) the downloaded files.
Once again - I never met such problem on the shared hostings before (but all them were under cPanel).

Please, any ideas what settings in PHP or Apache or Plesk or Linux or whatever I could try to adjust to solve the problem

Thank you very much in advance !