When you validate an empty string with the rules not_empty and min_length, validation passes.

Kohana Validation

public function action_index()
{
	echo "<h1>Validation checking</h1>";

	$data = array(
	    "contact_name"  => "Name here",
	    "contact_email" => "admin@example.co.uk",
	    "company_name"  => "Newco Inc",
	    "password"      => "",
	    "site_name"     => "Newco Inc",
	    "site_address"  => "newco",
	    "domain_name"   => "",
	    "agree"         => "agree",
	);

	$v = Validation::factory($data);

	$v->rules(
		'contact_email', array(
			array('Valid::email'),
			array('Valid::min_length', array(':value', 8)),
		)
	);
	$v->rules('password', array(
		array('Valid::not_empty'),
		array('Valid::min_length', array(':value', 5))
	));

	echo Debug::vars($v->check());

	echo Debug::vars($data);

}

Expected validation to fail, but it returns TRUE.