I have an issue with my plugin. I run an function if the plugin is activating this function include a file. But if I activate the plugin the file is included twice. Is this normal or an bug in WordPress? Is there an solution for this?

In the main file I do this

if ( file_exists ( dirname( __FILE__ ) . '/autoload/autoloader.php' ) )
{
    require_once dirname( __FILE__ ) . '/autoload/autoloader.php';
}