Incenteev/ParameterHandler in version 2.1@dev (on date 09/01/13) does not seem to support more than one depth level

ACTUAL_OUTPUT

Some parameters are missing. Please provide them.
extensions ({ Behat\Symfony2Extension\Extension: { mink_driver: true }, Behat\MinkExtension\Extension: { base_url: 'http://motivation-application.local/', default_session: symfony2 } }): ^Ĉ

behat.yml

default:
    extensions:
        Behat\Symfony2Extension\Extension:
            mink_driver: true
        Behat\MinkExtension\Extension:
            base_url: http://motivation-application.local/
            default_session: 'symfony2'

composer.json

{
    "require": {
        "php": ">=5.3.3",

        "incenteev/composer-parameter-handler": "~2.1@dev",
    },
    "extra": {
        "incenteev-parameters": [
            {
            "file": "app/config/parameters.yml"
            },
            {
                "file": "behat.yml",
                "parameter-key": "default"
            }
        ]
    }
}

EXPECTED_OUTPUT

Some parameters are missing. Please provide them.
extensions.Behat\Symfony2Extension\Extension.mink_driver (true): ^Ĉ