IndexController.php

public function testZfIssue4619Action()
{
    $form = new \Application\Form\Issue4619();
    $form->setData(array('testDateTime' => 'asdf'));
    // false
    Debug::dump($form->isValid());
    // 3 validators : Zend\Validator\NotEmpty, Zend\Validator\Date, Zend\Validator\DateStep
    Debug::dump($form->getInputFilter()->get('testDateTime')->getValidatorChain()->getValidators());

    $form = new \Application\Form\Issue4619();
    $form->getInputFilter()->get('testDateTime')->setRequired(true);
    $form->setData(array('testDateTime' => 'asdf'));
    // false
    Debug::dump($form->isValid());
    // 3 validators : Zend\Validator\NotEmpty, Zend\Validator\Date, Zend\Validator\DateStep
    Debug::dump($form->getInputFilter()->get('testDateTime')->getValidatorChain()->getValidators());

    $form = new \Application\Form\Issue4619();
    $form->getInputFilter()->get('testDateTime')->setRequired(false);
    $form->setData(array('testDateTime' => 'asdf'));
    // false
    Debug::dump($form->isValid());
    // 3 validators : Zend\Validator\NotEmpty, Zend\Validator\Date, Zend\Validator\DateStep
    Debug::dump($form->getInputFilter()->get('testDateTime')->getValidatorChain()->getValidators());

    $form = new \Application\Form\Issue4619();
    $form->setInputFilter(new \Application\Form\IssueFilter4619());
    $form->setData(array('testDateTime' => 'asdf'));
    // true -> not correct
    Debug::dump($form->isValid());
    // 1 validator only : Zend\Validator\NotEmpty
    Debug::dump($form->getInputFilter()->get('testDateTime')->getValidatorChain()->getValidators());
}

Issue4619.php

<?php
namespace Application\Form;

class Issue4619 extends \Zend\Form\Form
{
    public function __construct($name = null, $options = array())
    {
        parent::__construct($name, $options);

        $this->add(new \Zend\Form\Element\DateTime('testDateTime', array(
            'label' => 'Test datetime'
        )));
    }
}

IssueFilter4619.php

<?php
namespace Application\Form;

class IssueFilter4619 extends \Zend\InputFilter\InputFilter
{
    public function __construct()
    {
        $testDateTime = new \Zend\InputFilter\Input('testDateTime');
        $testDateTime->setRequired(true);

        $this->add($testDateTime);
    }
}