mixing:appendmediaentry not working for audio in SaaS (Eagle)

To reproduce use the test me console or this script:

<?php
require_once('lib/KalturaClient.php');
$config = new KalturaConfiguration($partnerId);
$config->serviceUrl = 'http://www.kaltura.com/';
$client = new KalturaClient($config);
$mixEntryId = null;
$mediaEntryId = null;
$client->setKs('yourKS');
$mixEntryId = 'a_mix_entry_of_your_own';
$mediaEntryId = 'an_audio_entry';
$results = $client-> mixing ->appendMediaEntry($mixEntryId, $mediaEntryId); ?>

This does not return an error but the audio is not included in tag nor visible with the KSE.

thx a lot