Composer removes web/bundles even if in .gitignore - symfony

Question

Ok, starting from this morning composer update removes all the assets from web/bundles.
It never did it before. I've searched here and i've found this link so i've checked my .gitignore (I can't find a .svnignore), here it is.
How can i solve?
/app/config/parameters.yml
/build/
/phpunit.xml
/var/*
!/var/cache
/var/cache/*
!var/cache/.gitkeep
!/var/logs
/var/logs/*
!var/logs/.gitkeep
!/var/sessions
/var/sessions/*
!var/sessions/.gitkeep
!var/SymfonyRequirements.php
/vendor/
/web/bundles/
[ EDIT ]
This is my composer.json, it did never delete the content of web/bundles folder. The only difference is that it upgraded symfony from 3.3.2 to 3.3.3
{
"name": "app/demo",
"license": "proprietary",
"type": "project",
"autoload": {
"psr-4": {
"": "src/"
},
"classmap": [
"app/AppKernel.php",
"app/AppCache.php"
]
},
"autoload-dev": {
"psr-4": {
"Tests\\": "tests/"
},
"files": [
"vendor/symfony/symfony/src/Symfony/Component/VarDumper/Resources/functions/dump.php"
]
},
"require": {
"php": ">=5.5.9",
"commerceguys/addressing": "^1.0.0-beta3",
"doctrine/doctrine-bundle": "^1.6",
"doctrine/doctrine-cache-bundle": "^1.2",
"doctrine/orm": "^2.5",
"egulias/email-validator": "^2.1",
"fdisotto/partita-iva": "^3.0",
"friendsofsymfony/user-bundle": "^2.0",
"incenteev/composer-parameter-handler": "^2.0",
"intervention/image": "^2.3",
"jstayton/google-maps-geocoder": "^2.4",
"knplabs/knp-menu-bundle": "^2.1",
"leafo/scssphp": "^0.6.7",
"misd/phone-number-bundle": "^1.2",
"sensio/distribution-bundle": "^5.0",
"sensio/framework-extra-bundle": "^3.0.2",
"symfony/assetic-bundle": "^2.8",
"symfony/monolog-bundle": "^3.0.2",
"symfony/polyfill-apcu": "^1.0",
"symfony/swiftmailer-bundle": "^2.3.10",
"symfony/symfony": "3.3.*",
"twig/twig": "^1.0||^2.0",
"usu/codice-fiscale": "^1.0"
},
"require-dev": {
"sensio/generator-bundle": "^3.0",
"symfony/phpunit-bridge": "^3.0"
},
"scripts": {
"symfony-scripts": [
"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::prepareDeploymentTarget"
],
"post-install-cmd": [
"#symfony-scripts"
],
"post-update-cmd": [
"#symfony-scripts"
]
},
"config": {
"sort-packages": true
},
"extra": {
"symfony-app-dir": "app",
"symfony-bin-dir": "bin",
"symfony-var-dir": "var",
"symfony-web-dir": "web",
"symfony-tests-dir": "tests",
"symfony-assets-install": "relative",
"incenteev-parameters": {
"file": "app/config/parameters.yml"
},
"branch-alias": null
}
}