Error with email class in CI 3.1.8

./system/libraries/Form_validation.php

PHP Code:

    /**
     * Valid Email
     *
     * @param    string
     * @return    bool
     */
    public function valid_email($str)
    {
        if (function_exists('idn_to_ascii') && preg_match('#\A([^@]+)@(.+)\z#', $str, $matches))
        {
            $domain = defined('INTL_IDNA_VARIANT_UTS46')
                ? idn_to_ascii($matches[2], 0, INTL_IDNA_VARIANT_UTS46)
                : idn_to_ascii($matches[2]);
            $str = $matches[1].'@'.$domain;
        }

        return (bool) filter_var($str, FILTER_VALIDATE_EMAIL);
    } 


Now you can see that it is checking the email domain.

im using the same validation rule in another CI 3.1.5 and it works perfect. but i have this issue on my new project with CI 3.1.8 !

the domain of the entered email is @gmail.com and i tested with my @icloud.com email. but keep showing error that i must enter valid email address !

i have google it and some people reported this as a bug. is it a bug?