def tree_post_save_handler(sender, instance, **kwargs):
    """
    Clobber the _ct_inventory attribute of this object and all sub-objects
    on save.
    """
    # TODO: Does not find everything it should when ContentProxy content
    # inheritance has been customized.
    instance.get_descendants(include_self=True).update(_ct_inventory=None)

    Clobber the _ct_inventory attribute of this object and all sub-objects
    on save.
    
feincms/extensions/ct_tracker.py