Symfony date formats are hard coded to the core and the definition is located at lib/symfony/i18n/sfDateFormat.class.php

This is how Symfony handles the date format definitions:

  protected $tokens = array(

And here's the reformating to the Javascript language (used for popup Date plugin)

array('yyyy' => 'Y', 'yy'=>'y', 'MM' => 'm', 'M'=>'m', 'dd'=>'d', 'd'=>'e', 'HH'=>'H', 'H'=>'k', 'hh'=>'I', 'h'=>'l', 'mm'=>'M', 'ss'=>'S', 'a'=>'p')

To change the format of a date for the object_input_date_tag you need to use parameter 'format' ⇒ 'd-M-Y' in the options.

object_input_date_tag($sklad, 'getCreatedAt', array (
  'rich' => true,
  'withtime' => false,
  'calendar_button_img' => '/sf/sf_admin/images/date.png',
  'control_name' => 'sklad[created_at]',
  'format' => 'd-G-yy',