Bug with MailPoet API adding subscribers

Collins From MailPoet. Our customer reported our form not saving subscribers against a list. Subscribers are being added but not being added to a list.

We use this code

$options = array(
‘send_confirmation_email’ => $this->is_double_optin(),
‘schedule_welcome_email’ => $this->is_welcome_message()
);

if (\MailPoet\Models\Subscriber::findOne($this->email)) {
\MailPoet\API\API::MP(‘v1’)->subscribeToList($this->email, $list_id, $options);

} else {
\MailPoet\API\API::MP(‘v1’)->addSubscriber($subscriber_data, [$list_id], $options);
}

I am sure $list_id is a valid list ID in integer.

I have confirmed this is a bug. Could you please check and possibly provide a fix?