Bug with inherited models

[Stranger6667]

Hello!
I have following setup (based on django-hstore test setup):

class HStoreModel(models.Model):
    objects = hstore.HStoreManager()

    class Meta:
        abstract = True


class SerializedDataBag(HStoreModel):
    name = models.CharField(max_length=32)
    data = hstore.SerializedDictionaryField()


class InheritedSerializedDataBag(SerializedDataBag):
    extra_data = models.CharField(max_length=32)

I've tried to create & modify some data but get this:

>>> instance = InheritedSerializedDataBag.objects.create(extra_data='Test')
>>> instance.data = {'foo': 'bar'}
>>> instance.save()
>>> InheritedSerializedDataBag.objects.all()

Traceback (most recent call last):
  File "/Users/dmitrijdygalo/repos/django-hstore/tests/django_hstore_tests/tests/test_serialized_dictionary_field.py", line 469, in test_inherited_model
    instance = InheritedSerializedDataBag.objects.get(id=instance.id)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/manager.py", line 92, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/query.py", line 351, in get
    num = len(clone)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/query.py", line 122, in __len__
    self._fetch_all()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/query.py", line 966, in _fetch_all
    self._result_cache = list(self.iterator())
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/query.py", line 275, in iterator
    obj = model(*row_data)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/base.py", line 382, in __init__
    setattr(self, field.attname, val)
  File "/Users/dmitrijdygalo/repos/django-hstore/django_hstore/descriptors.py", line 35, in __set__
    if value and self.field._from_db(obj):
  File "/Users/dmitrijdygalo/repos/django-hstore/django_hstore/fields.py", line 264, in _from_db
    return bool(model_instance._state.adding and model_instance.pk)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/base.py", line 509, in _get_pk_val
    return getattr(self, meta.pk.attname)
AttributeError: 'InheritedSerializedDataBag' object has no attribute 'serializeddatabag_ptr_id'

However in database data is not corrupted. Pointer to base table is OK, and data is also OK.
I use postgresql 9.4.1 and Django 1.7.9 during tests.
Here is test case for that. I'll try to find out why it happens, but I'm pretty new to codebase, so if anyone can help to fix this bug, it will be great :)

Cheers!