so this is funny. I think I managed to set IsBackendUser manually via code, in my custom RegistrationForm like this:
protected override bool TryCreateUser(UserManager manager, out User user, out MembershipCreateStatus status)
user = manager.CreateUser((string)this.UserNameField.Value, (string)this.PasswordField.Value, (string)this.EmailField.Value, null, null, !this.SendRegistrationEmail, null, out status);
user.IsBackendUser = false;
return (status == MembershipCreateStatus.Success);
1. not sure if its right, though, but in DB field sf_Users.is_backend_user = 0
2. But, when I go to backend and view that user, the checkbox 'this user can access backend' is checked, and grayed
3. Additionally, when I try to login with two such users (with this manually removed backend flag) it works.
Btw. this is valid for Small business edition.
Please can you confirm whether you can reproduce it and if it's a bug?