strange question when i access related object

My EventDate model has a ForeignKey to Event shown as follows:

class EventDate( models.Model ): # {{{1
    """ stores dates for events """
    eventdate_name = models.CharField(
            _( u'Name' ), blank = False, null = False,
            max_length = 80, help_text = _(
            "Example: call for papers" ) )
    eventdate_date = models.DateField( _( u'Date' ), blank = False,
            null = False, db_index = True, validators = [validate_year] )
    event = models.ForeignKey( Event, related_name = 'dates' )
    objects = models.GeoManager()

The shell output is:
In [10]: event.dates.create(eventdate_name='start', eventdate_date=datetime.date.today())
Out[10]: <EventDate: 2014-11-27    start>
In [11]: event.dates.all()
Out[11]: []

Why is event.dates.all() empty?

Does anyone have some advance?

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