I have found that addressbook entries occassionally vanish and have
discovered the following:
1. the addressbook will not display contacts that have one or more
addresses but none of them are marked as the preferred address
2. if you remove and address from a contact and leave one or more
addresses, the preferred selection will display at one of the other
addresses but doesn't actually save it that way unless you edit that
address and save it as the preferred address
Every once in a while I use set ALL the addresses as being preferred by
using UPDATE phpgw_contact_addr SET preferred='Y' .. note that this
nullifies the feature of having a preferred address.