Symfony 2.3登录表单是'；t身份验证

我正试图用Symfony2.3实现一个相当基本的登录表单，但我遇到了一个错误，有时在提供正确的凭据后重定向到期望的页面，但有时没有（相反，我只是重定向回登录页面）。这是我的security.yml文件：

security:
    encoders:
        Symfony'Component'Security'Core'User'User: plaintext
        Acme'MyBundle'Entity'User: sha512
    providers:
        main:
            id: acme.user.provider
    firewalls:
        dev:
            pattern: ^/(_(profiler|wdt)|css|images|js)/
            security: false
        login_firewall:
            pattern: ^/login$
            security: false
        secured_area:
            pattern: ^/
            form_login: ~
            logout:
                path:   /logout
                target: /
    access_control:
        - { path: ^/login$, roles: IS_AUTHENTICATED_ANONYMOUSLY, requires_channel: https }
        - { path: ^/, roles: ROLE_USER, requires_channel: https }

这是我的SecurityController:

<?php
namespace Acme'MyBundle'Controller;
use Sensio'Bundle'FrameworkExtraBundle'Configuration'Route;
use Sensio'Bundle'FrameworkExtraBundle'Configuration'Template;
use Symfony'Component'HttpFoundation'Request;
use Symfony'Component'Security'Core'SecurityContextInterface;
/**
 * Class SecurityController
 * @package Acme'MyBundle'Controller
 *
 * @Route("/")
 */
class SecurityController extends Controller
{
    /**
     * @param Request $request
     * @return 'Symfony'Component'HttpFoundation'Response
     *
     * @Route("/login", requirements={"_scheme" = "https"}, path="login")
     */
    public function LoginAction(Request $request)
    {
        $session = $request->getSession();
        // get the login error if there is one
        if ($request->attributes->has(SecurityContextInterface::AUTHENTICATION_ERROR)) {
            $error = $request->attributes->get(
                SecurityContextInterface::AUTHENTICATION_ERROR
            );
        } elseif (null !== $session && $session->has(SecurityContextInterface::AUTHENTICATION_ERROR)) {
            $error = $session->get(SecurityContextInterface::AUTHENTICATION_ERROR);
            $session->remove(SecurityContextInterface::AUTHENTICATION_ERROR);
        } else {
            $error = '';
        }
        // last username entered by the user
        $lastUsername = (null === $session) ? '' : $session->get(SecurityContextInterface::LAST_USERNAME);
        return $this->render(
            'AcmeMyBundle:Security:login.html.twig',
            array(
                // last username entered by the user
                'last_username' => $lastUsername,
                'error'         => $error,
            )
        );
    }
    /**
     * @Route("/login_check", requirements={"_scheme" = "https"}, path="login_check")
     */
    public function LoginCheckAction()
    {
    }
    /**
     * @Route("/logout", requirements={"_scheme" = "https"}, path="logout")
     */
    public function LogoutAction()
    {
    }
}

这是我的捆绑包的routing.yml文件：

_security:
    resource: "@AcmeMyBundle/Controller/SecurityController.php"
    type: annotation

当我提供正确的凭据时，大约20%的时间我会正确登录/重定向到给定的URL。其他80%的时间我只是被重定向回表单登录页面，没有错误消息。当我尝试使用不正确的凭据登录时，我也没有看到任何错误消息。

更新：问题似乎是Symfony在我的数据库中为每个请求创建了多个会话。我正在使用pdo处理程序。