I'm not sure I really have an answer for you, but I would say what you are experiencing
now is normal and there was a bug
previously.
I've often come across programs that won't yield easily and just say "access denied", even as an administrator. Often they are tied to services, and I believe you have to have special privileges for that. If it was easy to kill, a malware could exploit that fact and infect a machine by killing the processes.
I think self-defense is for defending against shutdown through the GUI and not related to the task manager process.
I'm sorry to say that you might have to find an alternative troubleshooting test