Thanks for adding details.
I could reproduce several time so this is what I had, did and what happened:
- I have a user tracker to store users information.
- For this to work (user register = create a Tiki user and an item in the tracker users) username field is set with auto assign (and show realname... if it has some importance)
- I set a group selector field and it was used to move a user from the register group (default) to the relevant group the user should be.
- Each time I edited this field on a user item but logged as admin on save, admin user preferences were changed.
During the tests to reproduce, i could easily reproduce by changing the admin real name preference (system administrator) that was changed for the last user edited real name (Arnold Conan). Once (as you know) my administrator user lost Admins group as I edited another user group using the field.
Nevertheless, I believe it is our responsibility to remind a Tiki user, like Vincent, asking for support that he can experiment, but should first take care to have a backup plan (like a secondary user and a real backup of the database) in case things turns bad while playing with users and groups (permissions and access).
Not all, depending their hosting, have backup and/or access to everything in the server to fix it (ssh, mysql database, etc) 😉