Why won't the address autocomplete when I'm adding a user to a Contacts group?

1) Using the button "Add to <group>" only autocompletes addresses from "My Contacts" and "Most Contacted" (NOT "Other Contacts" nor "Directory").
2) If your Contacts were imported into Google Apps, you must first use the address in a Gmail interface before autocompletion of it will work. For example, if your Contacts were imported from Exchange, once you use an address to send Google Mail it will autocomplete from then on in Mail, Contacts and other apps.
Below are some links that contain more information on autocompletion and Contacts: