Exception thrown when using alternative user provider/login handler

When using an alternative user provider / login (FOSUserBundle) handler as per documentation at https://doc.ez.no/display/EZP/How+to+authenticate+a+user+with+multiple+user+providers and https://github.com/FriendsOfSymfony/FOSUserBundle/blob/1.3.x/Resources/doc/index.md , some internal redirects (such as redirect to login, failed login_check, etc) will cause an exception.

It appears the SiteAccess/Router expects a siteaccess string and is receiving an object instead.

Steps to reproduce:

1. Install and configure FOSUserBundle as documented
   1. configure firewall

      security:
          providers:
              fos_userbundle:
                  id: fos_user.user_provider.username
          firewalls:
              fos_user_firewall:
                  pattern:   ^/
                  anonymous: ~
                  provider:  fos_userbundle_provider
                  form_login:
                      provider:      fos_userbundle
                      login_path:    login
                      check_path:    login_check
                      default_target_path: /
                  logout:
                      path:       logout
                      target:     /
          access_control:
              - { path: ^/login$, role: IS_AUTHENTICATED_ANONYMOUSLY }
              - { path: ^/register, role: IS_AUTHENTICATED_ANONYMOUSLY }
              - { path: ^/resetting, role: IS_AUTHENTICATED_ANONYMOUSLY }
              - { path: ^/admin/, role: ROLE_ADMIN }
      

2. Create a new user

   php ezpublish/console fos:user:create testuser
   

3. Try to login with an invalid password (if all is properly configured, login with valid credentials should still work).

Stack trace attached.