Hi Mary, thank you.
I did read both those posts from Helen and Iñaki.
It does work though... I have another site where it's working fine. We have a situation where safety administrators create accounts for their employees simply by using the 'create new account' link on the login page. The site where it does work is actually running a slightly older version of Moodle 3. The one where it's only working for manual accounts is running the latest stable version that was available on Monday of this week.
Sorry, I'm not trying to be crusty, it's just frustrating trying to figure out what the difference is.
