FOSOAuthServerBundle configuration issue

Question

I am building an app with angularjs frontend and symfony backend with the help of FOSOAuthServerBundle and FOSUserBundles for security.

Registration works fine but logging back in has an issue. When you provide your username/ password, authentication works fine and a token is generated but then a login form is presented to the user again to log in when they try to access a resource using the token.

I know it's a misconfiguration somewhere hoping someone will have the eye to point it our for me ;-)

security.yml

security:
encoders:
    AppBundle\Entity\User:
        algorithm:        sha1
        encode_as_base64: false
        iterations:       1

role_hierarchy:
    ROLE_ADMIN:       ROLE_USER
    ROLE_SUPER_ADMIN: ROLE_ADMIN

providers:
    fos_userbundle:
        id: fos_user.user_provider.username


firewalls:
    dev:
        pattern:  ^/(_(profiler|wdt)|css|images|js)/
        security: false

    oauth_token:
        pattern:    ^/oauth/v2/token
        security:   false

    oauth_authorize:
        pattern:    ^/oauth/v2/auth
        form_login:
            provider: fos_userbundle
            check_path: _security_check
            login_path: _demo_login
        anonymous: true

    main:
        pattern: ^/
        form_login:
            provider: fos_userbundle
            csrf_provider: form.csrf_provider
        logout:       true
        anonymous:    true

    api:
        pattern:    ^/api
        fos_oauth:  true
        stateless:  true


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 }
    - { path: ^/api, roles: [ IS_AUTHENTICATED_FULLY ] }

config.yml

fos_user:
    db_driver: orm
    firewall_name: main
    user_class: AppBundle\Entity\User

fos_oauth_server:
    db_driver: orm
    client_class:        AppBundle\Entity\Client
    access_token_class:  AppBundle\Entity\AccessToken
    refresh_token_class: AppBundle\Entity\RefreshToken
    auth_code_class:     AppBundle\Entity\AuthCode
    service:
        user_provider: fos_user.user_manager
        options:
            supported_scopes: user