It's the function web_delete() in /root/ispconfig/scripts/lib/config.lib.php. But you can check the logfile first: /home/admispconfig/ispconfig/ispconfig.log.
Ok the logfile looks fine, but it doesn't show creating/deleting users/groups.
im finding hard to understand the web_delete() function too, I can see where it backs up the website then removes it, and then backs up mysql and then deletes that, but I can't find exactly where it removes the group.
Can you help me further please ?