Front end users automatically adding to group

[scotch33]

Curiously, when either (in admin) creating a new Front End User or editing a new front end user, it's automatically ticking a user group box.

I have checked settings and changed "Require membership in at least one group:" to 'non' and set the below group to 'none', plus cleared cache. Additionally I have compared to another site with FEU to confirm the settings. All looks the same.

I must be missing something, but I can't see for looking. Anyone else got any ideas?

core 2.1.5 / feu 2.2.0.6