Zend Framework/Form: custom elements not shown on error

array(13) { ["customer"]=> string(1) "1" ["product"]=> string(2) "83" ["media"]=> string(1) "1" ["contact"]=> string(1) "1" ["date"]=> string(0) "" ["comment"]=> string(0) "" ["return"]=> string(1) "0" ["submit"]=> string(22) "Teststellung erstellen" ["csrf"]=> string(32) "97ce4374b92417c54013230126cb9d9c" ["id"]=> string(0) "" ["received"]=> string(0) "" ["finishedclipping"]=> string(0) "" ["returned"]=> string(0) "" }