Running a Single Exchange 2007 Ver. 8.03.0083.000 using all roles.
Database size > 100 users.
After disabling an account and hiding it from the Exchange Address Lists, it will sometimes randomly clear the attribute and show back up in the GAL months later. We have had users show back up and looking at the mailbox properties the "Hide from Exchange Address List" box is not checked. I am the only one administering the server and this has happened to some mailboxes several times.
Applying the settings again do remove the account from the OAB, and the GAL, so they are updating fine. Then at random, as sometimes its a couple weeks, or a couple months, or even six months, a few disabled users will show back up and I have to re-check the Hide box.