South doesn't recognize modification in ManytoMany fields

I have made a model change from

standard = models.ManyToManyField(Standard)

to

standard = models.ManyToManyField(Standard, blank = True, null = True)

South schemamigration for this app doesn't recognize the change ?

http://stackoverflow.com/questions/18243039/south-migrating-foriegn-key-many-to-many-field-to-null-true-blank-true-doesnt

Similar to the question link below, it's unanswered !

South migrations and changes to many-to-may fields

any idea? Please help ! 

--
You received this message because you are subscribed to the Google Groups "Django users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to django-users+unsubscribe@googlegroups.com.
To post to this group, send email to django-users@googlegroups.com.
Visit this group at http://groups.google.com/group/django-users.
For more options, visit https://groups.google.com/groups/opt_out.