Custom fields not working with Relationship API

1. Relationship API does not add custom field.
This is a piece of my codes for adding a relationship:

#############
$relationship_params = array(
'contact_id_a' => $data['contact_a'],
'contact_id_b' => $data['new_branch_id'],
'relationship_type_id' => $this->relationship_type_id,
'start_date' => array('d'=>$r_end_date[0],'M'=>$r_end_date[1],'Y'=>$r_end_date[2]),
'is_active' => 1,
'custom_56' => "test custom field"
);

2. Relationship api - civicrm_contact_relationship_get - fails to retrieve custom data that is attached to a relationship.

• CRM_Core_BAO_CustomGroup::getTree is using old param format (missing $form param 2)
• CRM_Core_BAO_CustomGroup::formatGroupTree is required prior to CRM_Core_BAO_CustomGroup::setDefaults

$new_relationship = & civicrm_relationship_create( $relationship_params );
############

#The custom field wasn't added through this params.

It looks like formating the custom data function not in api/v2/Relationship.php.