https://confluence.ez.no/display/EZP51/Legacy+code+and+features#Legacycodeandfeatures-UsingeZPublish5andSymfonyfeaturesinLegacy

If the controller executed makes use of runLegacyCallback, things will get ugly.

Real example: Legacy calls a controller which uses eZFind and thus also runCallback.

    public function runCallback( \Closure $callback, $postReinitialize = true )
    {
        $this->enterLegacyRootDir();
        $return = parent::runCallback( $callback, $postReinitialize );
        $this->leaveLegacyRootDir();
        return $return;
    }

The culprit can been seen here. First one enters the legacy-directory, and all is good. Then leaveLegacyRootDir() puts the script in the web-directory. The remaining legacy code executed after the Symfony-controller will then be executed within the wrong working directory. This causes all sorts of fun to happen. Crashing code, ini-cache-corruption...

The ini-cache corruption causes the setup-wizard to be displayed; even in an production environment. Needless to say, this is very much unwanted.

The code above should simply store the current working-directory and then restore it.