filefield_feeds_set_target not beeing invoked

The function filefield_feeds_set_target is not beeing invoked resulting in no file beeing downloaded. Other CCK fields are working as expected. Using custom parser based on FeedsParser, it just a skeleteon with two mapping sources, title and file.

public function parse(FeedsImportBatch $batch, FeedsSource $source) {
$string = $batch->getRaw();
$xml = simplexml_load_string($string);
foreach($xml->item as $item) {
$row = array(
'title' => 'Title',
'file' => array(
new FeedsEnclosure('http://localhost/feeds/sites/default/files/image.jpg', 'application/octet-stream'),
),
);
$batch->addItem($row);
}
$batch->setTitle('Test');
}