first i tried to set "php_value include_path ..." from a .htaccess file.
then it has been read into include_path by php, but it said
"Failed opening '...' for inclusion" for every file include()'d
from that directory.

then i tried the same from httpd.conf, then from php.ini.
in both cases the result was the same as with .htaccess
plus a coredump:

Core was generated by `/usr/sbin/apache-ssl'.
Program terminated with signal 11, Segmentation fault.

#0  0x401cf927 in free () from /lib/libc.so.6
#1  0x4040a0c8 in cfg_get_string () from /usr/lib/apache/1.3/libphp4.so
#2  0x4042efa3 in zend_hash_destroy () from /usr/lib/apache/1.3/libphp4.so
#3  0x4040a3de in php_shutdown_config () from /usr/lib/apache/1.3/libphp4.so
#4  0x404092f8 in php_request_shutdown () from /usr/lib/apache/1.3/libphp4.so
#5  0x40409649 in php_module_shutdown () from /usr/lib/apache/1.3/libphp4.so
#6  0x40409620 in php_module_shutdown_wrapper () from /usr/lib/apache/1.3/libphp4.so
#7  0x40437d1d in php_xbithack_handler () from /usr/lib/apache/1.3/libphp4.so
#8  0x8054ffc in ap_run_cleanup ()
#9  0x8054074 in ap_clear_pool ()
#10 0x80540d4 in ap_destroy_pool ()
#11 0x8054060 in ap_clear_pool ()
#12 0x80540d4 in ap_destroy_pool ()
#13 0x805dd60 in ap_exists_scoreboard_image ()
#14 0x8060165 in ap_child_terminate ()
#15 0x80605ad in main ()
#16 0x40198a12 in __libc_start_main () from /lib/libc.so.6

i don't know if that is a bug or my fault in some way,
please forgive me if it is the latter.