Can't migrate to entity reference field

It seems that this should be completely straightforward (http://drupal.org/node/1536914) , but I can't get it to work.

I have two node migrations at the moment: clubs and athletes. Athletes is dependent on clubs, and clubs has already run successfully. The Athlete node contains an entity reference field, field_club, that points to Club nodes. In the migration class that handles Athletes, I have:

$this->addFieldMapping('field_club', 'club')
->sourceMigration('ImdClub');

I've verified that the value of club is correct. If I map club to another field using the same source migration parameter, I see the expected NID appear in that field. However, I can't get this value to migrate into the entity reference field, field_club. After the athlete migration, field_club is empty, i.e. no value for target_id at:

$node->field_club['und'][0]['target_id']

Do I need to do more than this to get entity reference to recognize the mapped value as the target_id?

Working with Migrate 7.x-2.5 and Entity Reference 7.x-1.0

Thanks in advance for any help or pointers for troubleshooting!

Dave