If account is subscribed to a forum (not to a topic), it'll get new topic notifications (newtopic_notify.txt) and replies notifications (topic_notify.txt). For the latter, the topic unsubscribe link will be provided an email message which produces error as a user isn't subscribed to the topic but to a forum. In this case, forum_notify.txt with the proper link is to be used, but it's never used at all in any email notifications.