delete rule set in abstract-document fails

I had a class something like this:

class Person(Document):
    name = StringField(verbose_name="Name")

class AbstractAddress(DynamicDocument):
    meta = {
        "abstract": True
    }
    person_ref = ReferenceField(Person, required=True, reverse_delete_rule=CASCADE)


class RealAddress(AbstractAddress):
     // stuff

The following code gives an error:

p = someperson
p.delete()

# AttributeError: type object 'AbstractAddress' has no attribute 'objects'

#  **filename*** in **methodname**
# 
#                 p.delete()
# 
#     ...
# 
# ▶ Local vars
# /usr/local/lib/python2.7/dist-packages/mongoengine/document.py in delete
# 
#                 self._qs.filter(**self._object_key).delete(write_concern=write_concern, _from_doc_delete=True)
# 
#     ...
# 
# ▶ Local vars
# /usr/local/lib/python2.7/dist-packages/mongoengine/queryset/base.py in delete
# 
#                     ref_q = document_cls.objects(**{field_name + '__in': self})
# 
#     ...

Note: i juggled some names around,, but you get the idea :)

When I define the ReferenceField in the non-abstract class the delete() call works

-- mongoengine installed using pip, its 0.8.7.

Start by reproducing the failure in mongoengine/document.py through the delete path shown in mongoengine/queryset/base.py. Check how the abstract AbstractAddress reference is resolved during Person deletion, then verify that deleting a Person with the inherited reference no longer raises AttributeError.