[web2py] requires IS_IN_SET()

[Chandrakant Kumar]

I'm adding extra fields to auth_user as,
        auth.settings.extra_fields['auth_user']= [
                Field('user_type', requires=IS_IN_SET('Admin', 'Staff'))]
But, in the Register form I'm getting a listbox with single letter options  
like, a, d, m, i, n.
Is there something missing?