Varios perfiles de usuario en django-userena

Estoy intentando hacer un perfil múltiple para Userena; cada usuario solo puede tener un tipo de perfil. Después de otras discusiones, estoy usando la herencia de varias tablas, pero cuando hago esto, no puedo guardar los datos en los modelos derivados. Todo termina siendo CommonProfile, que no debería ser posible / permitido. Código de ejemplo a continuación:

enmodels.py:

# models.py
# This is an example of how i've attempted to get 
# multiple user profiles working with Userena
from django.contrib.auth.models import User
from django.db import models
from userena.models import UserenaLanguageBaseProfile

class CommonProfile(UserenaLanguageBaseProfile):
    """Common fields for 2 user profiles: Spam and Eggs"""
    user = models.OneToOneField(User)
    common_field = models.CharField(max_length=100)

    @property
    def is_spam(self):
        """Find out if this is a Spam user"""
        try:
            self.spamprofile
            return True
        except SpamProfile.DoesNotExist:
            return False

    def get_real_type(self):
        """return the real model"""
        if self.is_spam:
            return self.spamprofile
        else:
            return self.eggsprofile

class SpamProfile(CommonProfile):
    spam_field = models.CharField(max_length=20)

class EggsField(CommonProfile):
    eggs_field = models.SmallIntegerField()

enforms.py

# forms.py
# This is the form to sign up a Spam Type Person

from django import forms
from userena.forms import SignupFormTos
from . models import CommonProfile, SpamProfile

class SpamSignupForm(SignupFormTos):
    """signup a Spam Person"""
    common_field = forms.CharField(label='what is your quest')
    spam_field = forms.CharField(label='what kind of spam are you')

    def clean(self):
        cleaned_data = super(SpamSignupForm,self).clean()
        #do stuf, same idea for clean_<field>
        return cleaned_data

    def save(self):
        """Save the SpamProfile"""
        user = super(SpamSignupForm,self).save()
        common_profile = user.get_profile()
        spam_profile = SpamProfile(commonprofile_ptr=common_profile)
        spam_profile.spam_field = self.cleaned_data['spam_field']
        spam_profile.save()
        return spam_profile

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