Symfony2 - PHP fatal error Class not found - composer-php

Question

I have a weird behaviour with my symfony2 project. A few days ago, I've tried to add a custom form listener which failed because symfony didn't find the namespace. <- Just for your information
I didn't work on this error, because I had some other things to do. Now, I wanted to add an VAT-Validator to my signup form and I was using
composer require ddeboer/vatin-bundle
to add this bundle to my project. It was working great in my dev-enviroment. Then, when I wanted to update my project on my staging-webserver with git and while clearing the cache with
php app/console cache:clear --env=prod
I get this message:
PHP Fatal error: Class 'Ddeboer\VatinBundle\DdeboerVatinBundle' not found in ../app/AppKernel.php on line 24
I have tried it with other bundles, too. But its the same error with every "new" bundle. Since, I have experienced the namespace problem just a few days before, I guess there is a problem with autoloading or something.
Already, tried various solution I have found on google and stackoverflow.
In the documentation, there is a hint:
If you get a "class not found" error during this step, you may need to run export SYMFONY_ENV=prod before running this command so that the post-install-cmd scripts run in the prod environment.
I am using windows and this command is not working. Also, on my ubuntu server I can use this command, but there seems to be no effect.
Here is my composer.json:
{
"name": "Admin/myproject",
"license": "proprietary",
"type": "project",
"autoload": {
"psr-0": {
"": "src/",
"SymfonyStandard": "app/"
}
},
"require": {
"php": ">=5.3.3",
"symfony/symfony": "2.7.*",
"doctrine/orm": "~2.2,>=2.2.3,<2.5",
"doctrine/dbal": "<2.5",
"doctrine/doctrine-bundle": "~1.2",
"twig/extensions": "~1.0",
"symfony/assetic-bundle": "~2.3",
"symfony/swiftmailer-bundle": "~2.3",
"symfony/monolog-bundle": "~2.4",
"sensio/distribution-bundle": "~3.0,>=3.0.12",
"sensio/framework-extra-bundle": "~3.0,>=3.0.2",
"incenteev/composer-parameter-handler": "~2.0",
"friendsofsymfony/elastica-bundle": "^3.2",
"elasticsearch/elasticsearch": "~1.0",
"cocur/slugify": "^2.0",
"ddeboer/vatin-bundle": "^2.0"
},
"require-dev": {
"sensio/generator-bundle": "~2.3",
"phpdocumentor/phpdocumentor": "~2.2"
},
"scripts": {
"post-root-package-install": [
"SymfonyStandard\\Composer::hookRootPackageInstall"
],
"post-install-cmd": [
"Incenteev\\ParameterHandler\\ScriptHandler::buildParameters",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::removeSymfonyStandardFiles",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::prepareDeploymentTarget"
],
"post-update-cmd": [
"Incenteev\\ParameterHandler\\ScriptHandler::buildParameters",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::removeSymfonyStandardFiles",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::prepareDeploymentTarget"
]
},
"config": {
"bin-dir": "bin"
},
"extra": {
"symfony-app-dir": "app",
"symfony-web-dir": "web",
"symfony-assets-install": "relative",
"incenteev-parameters": {
"file": "app/config/parameters.yml"
}
}
}