[horde] Horde PHP-FPM include_path mystery

[Admin Beckspaced]

Dear horde list users,

I'm running an opensuse 15.4 box with PHP-FPM 7.4.33 (yes I know it's EOL)

Horde is 5.2.23 with IMP 6.2.27

PEAR Horde is installed at /usr/share/php7/PEAR/

php.ini sets the include path = ".:/usr/share/php7:/usr/share/php7/PEAR"

as far as I know the delimiter : separates the different include paths
so I have 3 paths

. the current directoy
/usr/share/php7
/usr/share/php7/PEAR

and from what I remember PHP automatically tries to look for included 
files in all those 3 include paths

If I run Horde & IMP with the default php.ini include path I receive a 
Fatal Error

Class 'PEAR_Config' not found

If I then set a different path order via php-fpm pool configuration the 
fatal error is gone
I move the PEAR path before the php7 path

php_value[include_path] = ".:/usr/share/php7/PEAR:/usr/share/php7"

but I still don't get it.
Isn't PHP supposed to look at all given include_path one after the other?

If anyone could share some insights I would be more than grateful :)

thanks
& greeetings
Becki