django models recursive imports - how to resolve

I have a model project_phase:

    from django.db import models
    from django.utils import simplejson
    from core.models import pmo_review_task

it references pmo_review_task (because it creates a pmo_review_task in its save ovewrite)

from django.db import models
from datetime import datetime
from django.contrib.auth.models import User
from core.models import sc_review_task

which references sc_review_task that references project_phase (because it creates a project_phase in its save ovewrite)

from django.db import models
from core.models import project_phase

so it ends up project_phase imports pmo_review_task imports sc_review_task imports project_phase and I guess it loops up somehow generating this error:

Unhandled exception in thread started by <bound method Command.inner_run of <django.core.management.commands.runserver.Command object at 0x010ACFB0>>
Traceback (most recent call last):
  File "C:\Python27\lib\site-packages\django\core\management\commands\runserver.py", line 88, in inner_run
    self.validate(display_num_errors=True)
  File "C:\Python27\lib\site-packages\django\core\management\base.py", line 249, in validate
    num_errors = get_validation_errors(s, app)
  File "C:\Python27\lib\site-packages\django\core\management\validation.py", line 35, in get_validation_errors
    for (app_name, error) in get_app_errors().items():
  File "C:\Python27\lib\site-packages\django\db\models\loading.py", line 146, in get_app_errors
    self._populate()
  File "C:\Python27\lib\site-packages\django\db\models\loading.py", line 64, in _populate
    self.load_app(app_name)
  File "C:\Python27\lib\site-packages\django\db\models\loading.py", line 78, in load_app
    models = import_module('.models', app_name)
  File "C:\Python27\lib\site-packages\django\utils\importlib.py", line 35, in import_module
    __import__(name)
  File "C:\work\Portman\core\models\__init__.py", line 4, in <module>
    from pmo_review_task import pmo_review_task
  File "C:\work\Portman\core\models\pmo_review_task.py", line 5, in <module>
    from core.models import sc_review_task
  File "C:\work\Portman\core\models\sc_review_task.py", line 3, in <module>
    from core.models import project_phase
  File "C:\work\Portman\core\models\project_phase.py", line 4, in <module>
    from core.models import pmo_review_task
ImportError: cannot import name pmo_review_task

how do I overcome this?