Error on adding contact object to group through API

If we do this:
$contacts = crm_get_group_contacts($group, NULL);

We get an object (among others) that looks like this:
[5] => CRM_Contact_DAO_Contact Object
(
[id] => 10305
[domain_id] => 1
[contact_type] => Individual
[legal_identifier] =>
[external_identifier] =>
[sort_name] => Blah
[display_name] => Mr. Blah
[nick_name] =>
[snip[
[contact_id] => 167
[first_name] => Blah
[snip]
)

So far so good. However when we try and insert these contacts into a new group by doing something like this:
$result = crm_add_group_contacts($addedgroup, $contacts);

We get the following error:
Array
(
[callback] => Array
(
[0] => CRM_Core_Error
[1] => handle
)

[code] => -3
[message] => DB Error: constraint violation
[mode] => 16
[debug_info] => INSERT INTO civicrm_subscription_history (contact_id , group_id , date , method , status , tracking ) VALUES ( 10305 , 23 , 20060321202634 , 'Admin' , 'Added' , NULL ) [nativecode=1216 ** Cannot add or update a child row: a foreign key constraint fails]
[type] => DB_Error
[user_info] => INSERT INTO civicrm_subscription_history (contact_id , group_id , date , method , status , tracking ) VALUES ( 10305 , 23 , 20060321202634 , 'Admin' , 'Added' , NULL ) [nativecode=1216 ** Cannot add or update a child row: a foreign key constraint fails]
[to_string] => [db_error: message="DB Error: constraint violation" code=-3 mode=callback callback=CRM_Core_Error::handle prefix="" info="INSERT INTO civicrm_subscription_history (contact_id , group_id , date , method , status , tracking ) VALUES ( 10305 , 23 , 20060321202634 , 'Admin' , 'Added' , NULL ) [nativecode=1216 ** Cannot add or update a child row: a foreign key constraint fails]"]
)

As you can see - the subscription_history code is trying to use the civicrm_group_contact id as the contact_id. This of course fails (and in cases where it doesn't fail is broken anyway, as history for the wrong contact will be entered).

I am not sure where the problem is - it could be that crm_get_group_contacts is returning invalid CRM_Contact_DAO_Contact objects, or that crm_add_group_contacts is passing the wrong id downstream.

If it is the latter then it should be as simple as (Group.php, line 209)
foreach($contacts as $contact){
if ( ! isset( $contact->id ))

{ return _crm_error( 'Invalid contact object passed in' ); }
$contactID[] = $contact->id;
}
foreach($contacts as $contact){
if ( ! isset( $contact->contact_id )) { return _crm_error( 'Invalid contact object passed in' ); }

$contactID[] = $contact->contact_id;
}

However, this would of course break if crm_add_group_contacts should actually be expecting a contact object with id referencing contact_id as implied by http://wiki.civicrm.org/confluence/display/CRM/Data+Model#DataModel-ContactRef.

Hope this helps!