Primary key error for ManyToManyField in a legacy database

I have a legacy database setup like this:

class Team(models.Model):
id = models.AutoField(primary_key=True, db_column='TeamID')
name = models.CharField(max_length=100, db_column='TeamName')
groupings = models.ManyToManyField(Grouping,
related_name='groupings', db_table='teamgrouping')

class Grouping(models.Model):
id = models.AutoField(primary_key=True, db_column='GroupingID')
name = models.CharField(max_length=250, db_column='GroupingName',
unique=True)
class Meta:
db_table = 'grouping'
ordering = ['name']

class TeamGrouping(models.Model):
id = models.AutoField(primary_key=True,
db_column='teamgroupingID')
grouping = models.ForeignKey(Grouping, db_column='grouping_id')
team = models.ForeignKey(Team, db_column='team_id')
class Meta:
db_table = 'teamgrouping'
unique_together = (('grouping', 'team'), )

When I display the Team model for editing in the Admin interface, it
shows up OK. All the TeamGrouping's also show up, in a neat many-to-
many widget, via the "groupings" field.

However, when I try and save the entry, I get this error:

OperationalError at /admin/edit/team/42402/

(1054, "Unknown column 'teamgrouping.id' in 'field list'")

Request Method: POST
Request URL: http://127.0.0.1:8000/admin/edit/team/42402/
Django Version: 1.2.1
Exception Type: OperationalError
Exception Value:

(1054, "Unknown column 'teamgrouping.id' in 'field list'")

Exception Location: /usr/lib/pymodules/python2.6/MySQLdb/
connections.py in defaulterrorhandler, line 35

I am not sure (a) why Django is expecting to find a
"'teamgrouping.id'" (I assume because "id" is the default name of a
table's primary key field?) and (b) how to tell it to use
'teamgrouping.teamgroupingID' as the primary key (as specified in the
TeamGrouping class)?

Note: I am not using the "through" keyword because this is only needed
when there are additional fields that are required on the intermediate
table.

Thanks
Derek

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