Default value for managed file elements stopped submitting

Two days ago I upgraded from 7.28 to 7.29 and now my website has serious problems. Managed file form elements no longer submits it's default values. For example, this form worked perfectly and now does not:

    $form['function'][$item->idFunction] = array(
      'name' => array(
        '#title' => t('Function name'),
        '#title_display' => 'invisible',
        '#type' => 'textfield',
        '#size' => 30,
        '#maxlength' => 120,
        '#default_value' => $item->FunctionNameInner,
      ),
      'FunctionIcon' => array(
        '#type' => 'managed_file',
        '#title' => t("Function's function"),
        '#title_display' => 'invisible',
        '#upload_validators' => array(
          'file_validate_extensions' => array('gif png jpg jpeg'),
          'file_validate_size' => array(variable_get('mymodule_image_size', 5 * 1024 * 1024)),
        ),
        '#upload_location' => 'public://mymodule/function',
        '#default_value' => $item->FunctionIcon,
        '#required' => TRUE,
        '#theme' => 'preview_upload',
      ),
      
      'Important' => array(
        '#type' => 'checkbox',
        '#title' => t('Important'),
        '#title_display' => 'invisible',
        '#default_value' => $item->Important,
      ),

      'id' => array(
        '#type' => 'hidden',
        '#default_value' => $item->idFunction,
      ),
      
      'weight' => array(
        '#type' => 'weight',
        '#default_value' => isset($item->weight)?$item->weight:'',
        '#delta' => 100,
      ),
    );

When I submit this form without changing anything, default file IDs are in $_POST as expected, but they are no longer in $form_state['values']