The setter for a RelatedManager type attribute (reverse relation) of a Django model requires the value to be set to be a list even if it would consist of only one object like in this save_related method that is fixed in this commit. Otherwise, Django raises TypeError in django/db/models/fields/related.py __set__ of ForeignRelatedObjectsDescriptor:
Exception Value: add() argument after * must be a sequence, not MyModel
Tested in Django 1.4.2