Dlaczego aktualizacja zależności od kompozytora zajmuje do dwóch minut, nawet jeśli nie nastąpiły żadne zmiany?

A popularna sugestia to jest dodanie--prefer-dist flagę, którą dodałem do mojego polecenia:

php composer.phar update --prefer-dist

Ale to nie ma znaczenia. Poniżej znajduje się mój plik composer.json - czy brakuje mi czegoś oczywistego?

{
    "name": "my-namespace/symfony",
    "type": "project",
    "description": "",
    "require": {
        "php": ">=5.3.3",
        "symfony/symfony": "2.3.*",
        "doctrine/orm": ">=2.2.3,<2.4-dev",
        "doctrine/doctrine-bundle": "1.2.*",
        "twig/extensions": "1.0.*",
        "symfony/assetic-bundle": "2.3.*",
        "symfony/monolog-bundle": "2.3.*",
        "sensio/framework-extra-bundle": "2.3.*",
        "sensio/generator-bundle": "2.3.*",
        "sensio/distribution-bundle": "2.2.*",
        "my-namespace/my-bundle": "1.0.*"
    },
   "repositories": [
        {
            "type": "vcs",
            "url": "http://username:[email protected]/my-bundle.git"
        }
    ],    
    "scripts": {
        "post-install-cmd": [
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile"
        ],
        "post-update-cmd": [
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile"
        ]
    },
    "config": {
        "bin-dir": "bin"
    },
    "minimum-stability": "dev",
    "extra": {
        "symfony-app-dir": "app",
        "symfony-web-dir": "web",
        "branch-alias": {
            "dev-master": "2.3-dev"
        }
    }
}