不重定向到主页(索引.php）

我的代码有问题吗？它可以工作，但它不会重定向到我的索引.php它总是以表单所在的登录名.php结束。

    <?php
    include 'core/ini.php';
    if (empty($_POST) === false) {
        $username = $_POST ['username'];
        $password = $_POST ['password'];
        if (empty ($username) === true || empty ($password) === true ) {
            $errors[] = 'You need to enter a username and password!';
        } else if (user_exists($username) === false) {
            $errors[] = 'We can''t find that username. Have you registered?';
        } else if (user_active($username) === false) {
            $errors[] = 'You haven''t activated your account! ';
        } else {
            $login = login($username, $password) ;
            if ($login === false) {
                $errors[] = 'That username/password combination is incorrect ';
            } else {
                $_SESSION['user_id'] = $login;
                header('Location :index.php');
                exit();
            }
        }
        print_r($errors);
    }
    ?>
thanks!
EDIT *
this is my login.php 
<?php
include 'core/ini.php';
if (empty($_POST) === false) {
    $username = $_POST ['username'];
    $password = $_POST ['password'];
    if (empty ($username) === true || empty ($password) === true ) {
        $errors[] = 'You need to enter a username and password!';
    } else if (user_exists($username) === false) {
        $errors[] = 'We can''t find that username. Have you registered?';
    } else if (user_active($username) === false) {
        $errors[] = 'You haven''t activated your account! ';
    } else {
        $login = login($username, $password) ;
        if ($login === false) {
            $errors[] = 'That username/password combination is incorrect ';
        } else {
            $_SESSION['user_id'] = $login;
            header('Location :index.php');
            exit();
        }
    }
    print_r($errors);
}
?>

这就是过程的进行。我不知道我应该把我的开始会话放在哪里，但我不知道为什么它可以在没有错误的情况下工作。