Integration with django-reversion error

[prime51]

I am using django-reversion to support version control of model objects, and I followed the instructions from Third-party applications support in the doc. Below is the example from the doc:

class ModelAChildAdmin(PolymorphicChildModelAdmin, VersionAdmin):
    base_model = ModelA  # optional, explicitly set here.
    base_form = ...
    base_fieldsets = (
        ...
    )

class ModelBAdmin(ModelAChildAdmin, VersionAdmin):
    # define custom features here

class ModelCAdmin(ModelBAdmin):
    # define custom features here


class ModelAParentAdmin(VersionAdmin, PolymorphicParentModelAdmin):
    base_model = ModelA  # optional, explicitly set here.
    child_models = (
        (ModelB, ModelBAdmin), 			<---
        (ModelC, ModelCAdmin),			<---
    )

revisions.register(ModelB, follow=['modela_ptr'])
revisions.register(ModelC, follow=['modelb_ptr'])
admin.site.register(ModelA, ModelAParentAdmin)

An error occured

Exception has occurred: TypeError 
	issubclass() arg 1 must be a class

I guess it is due to the child_models attribute in ModelAParentAdmin class is assigned with a list of tuples, which actually requires a list of model classes.

If I fix that error by changing the child_models to child_models = ( ModelB, ModelC, ), then ModelB and ModelC are not registered in the admin site.

So my question is how can I integrate django-reversion with django-polymorphic. Any working examples are appreciated!

Thank you