The documentation says that the #prefix and #suffix properties are available for the file_managed FAPI element, but ~ line 470 of file.module these properties are overwritten:
<?php
// Prefix and suffix used for Ajax replacement.
$element['#prefix'] = '<div id="'. $element['#id'] . '-ajax-wrapper">';
$element['#suffix'] = '</div>';
?>It makes sense, but should this be handled in another way?