Validacne pravidlo a chybova sprava

Moja custom validacna funkcia by mala vratit chybovu spravu aj s hodnotou ziskanou pocas validacie. Priamo modifikovat spravu zadanu cez addRule() zrejme nie je mozne:

$form->addText('num1', 'Multiple of 8:')
    ->addRule('myValidator', 'First number must be %d multiple', 8);

Toto sluzi zrejme len na formatovanie.

Ak to ale vyriesim takto:

$form->addText('thumbnail_position', 'Pozicia na vytvorenie nahladu')
	->addRule(Form::FILLED, 'Zadajte poziciu')
	->addRule(array($this, 'ruleValidPosition'), null);


...


public function ruleValidPosition($control) {

	$control->getForm()->addError("Validation error message with value $value");
}

, tak v zozname chyb figuruje prazdna message z addRule() pre element, message z custom validacie a navyse warning:

PHP Warning: Illegal offset type in isset or empty in .../libs/Nette/Forms/Rules.php:66

Bug ?