Just chucking an idea into the pot.... If apache is restarted using apachectl script it first runs configtest before attempting a restart. If apache is restarted using /etc/init.d/httpd script it doesn't run configtest before attempting a restart. I think ISPConfig should run a configuration check before a restart (to prevent IPSConfig becoming unuseable.) The restart is triggered in server/mods-available/web_module.inc.php. If we included a config test before restarting, where would the sensible place be to report an error if it fails the config test?