On django==1.6

products.py

class ProductCategory(models.Model):
    name = models.CharField(max_length=50)
    priority = models.IntegerField()
    slug = models.CharField(max_length=50, unique=True)

    class Meta:
        ordering = ['priority']
        

class AbstractProduct(models.Model):
    categories = models.ManyToManyField(ProductCategory)
    
    class Meta:
        abstract=True


class Product(AbstractProduct):
    pass
    

class PlanSnapShot(AbstractProduct):
    name = models.CharField(max_length=255)
    base_discount = models.FloatField(null=True, blank=True)
    

# The following error is given when executing `<plansnapshot object>.categories.all()` with `<plansnapshot object>` being any instance of the class   
FieldError: Cannot resolve keyword u'plansnapshot' into field. Choices are: id, name, priority, product, slug

# Yet when I run the same code in `shell`.  The relationship works and no errors are thrown.  I am scratching my head here.

# Here is additional Information
# ##############################

# If I print `<plansnapshot object>.categories` they are the same in both the application and the shell. 

# I have tried importing both `Product` and `PlanSnapShot` and not importing the other.  Everything works in the shell regardless.

# `<product object>.categories.all()` works in the application and the shell.

# I have tried adding a generic property to `PlanSnapShot`.  I can access that property in both the application and the shell without having to restart the application.

# Tried putting unique many to many fields in the two inheriting models instead of the abstract class.  When running an --auto migration in south I get this return
 - Deleted model cart.GoldenPlan
 - Deleted model cart.PlanSnapShot
 - Deleted M2M table for categories on cart.PlanSnapShot
 - Deleted model cart.StoreDisplay