Symfony2安全组件和Propel，select语句中的表名不正确

Question

我阅读this page以使用propel orm管理我的symfony2.0登录表单。 在表单提交propel上返回此错误：

Warning! Unable to execute SELECT statement 
[SELECT admin.ID, admin.USERNAME, admin.PASSWORD, admin.USERLEVEL, admin.MERCATO_ID 
FROM `` `admin` WHERE admin.USERNAME=:p1 LIMIT 1] 
[wrapped: SQLSTATE[42000]: Syntax error or access violation: 1103 Incorrect table name '']

应该是

FROM admin

而不是

FROM `` `admin`

为什么在select语句中有``在表名admin之前？

编辑

security.yml内容

security:
    providers:
        custom_provider:
            id: papernet.secured.security.provider
    role_hierarchy:
        ROLE_ADMIN:       ROLE_USER
        ROLE_SUPER_ADMIN: [ROLE_USER, ROLE_ADMIN, ROLE_ALLOWED_TO_SWITCH]
    firewalls:
        dev:
            pattern:  ^/(_(profiler|wdt)|css|images|js)/
            security: false
        login_firewall:
          pattern:    ^/login$
          anonymous:  ~
        secured_area:
            pattern:  ^/
            anonymous: ~
            form_login:
                check_path: /login_check
                login_path: /login
            logout:
                path:   /logout
                target: /login
            #anonymous: ~
            #http_basic:
            #    realm: "Secured Demo Area"

    access_control:
      - { path: ^/login, roles: IS_AUTHENTICATED_ANONYMOUSLY }
      - { path: ^/, roles: ROLE_ADMIN }

papernet.secured.security.provider是我的自定义提供商，如指南

所示