I noticed that ISPConfig creates .php-fcgi-starter in /var/.../php-fcgi-scripts/ispconfig/ and /var/.../php-fcgi-scripts/webx/ folders. There are values called PHP_FCGI_CHILDREN and export PHP_FCGI_CHILDREN which shouldn't be used.
These values are meant for standalone fcgi server, not for mod_fastcgi or mod_fcgid which handle process creation by themselves. When used with mod_fastcgi or mod_fcgid, these values cause problems.
Am I correct in assuming that editing /usr/local/ispconfig/server/conf/php-fcgi-starter.master would make these changes default?
Edit: Apparently I am.
Edit 2: And apparently PHP_FCGI_MAX_REQUESTS should be set to 500 to prevent a probable race condition.