由于某种原因，我的header("Location: <url>")被重定向到了它原来的POST url，我不得不切换到回显javascript重定向，以使它暂时工作。

catch (Exception $e)
{            
    switch (get_class($e))
    {
        case 'ValidationError':
            $_SESSION['FLASH_ERROR'] = $e->getMessage();
            $location = CB_ABS_URI."upgrade?ID=".$_GET['ID']."&package=".$_POST['plan'];
            # die("You're getting redirected ... <script type='text/javascript'>setTimeout('redirect()',0); function redirect() { window.location = '$location'; }</script>");
            header("Location:", $location);
            exit;
        break;
        default:
            # die
        break;
    }            
}