What we applicants define as a Ghost Update is the arrival of an e-mail or a notification that your account has been updated, but when you log in it appears that your account is exactly the same as it was before the notification.
Some people speculate that they happen because an agent logs into your file and pokes around so the system generates a response on your account. If this is true, GUs can be a good sign, from the perspective that your file is being looked at.