problem with phprc var

hi.

i have some trouble with an php5 installation used by an apache2
webserver and the suphp wrapper.
when i want to use another php.ini for one of my vhosts and have set
it via "setenv phprc /path/to/the/php/ini/dir"

if i have an empty docroot with only one index.php including a
"phpinfo();" then the phpinfo will not parse the custom php.ini.
- the phprc var is set as wanted in the phpinfo output...

but if I create an !empty! php.ini in the docroot the custom php.ini
will get parsed and the phprc var is set also...

i have to create the php.ini file for every subdir.

and i am very confused ;-/

my versions:
debian squeeze
php 5.3.5-0.dotdeb.1
apache 2.2.16-6
suphp 0.7.1-1


thank you for your help