Here's an example that currently fails:
in config.php:

    $config['cookie_prefix'] = 'foo_';

then later:

    // there should be no prefix (e.g. cookie related to third-party code)
    $CI->input->set_cookie([
        'prefix' => '',
        'name'   => 'lename',
        'value'  => 'levalue',
        'expire' => 3600,
    ]);