For the record, in case others are following this thread, the question was also posed on the Legacy User Group mailing list. (legacyusergroup@legacyusers.com/msg21295.html" target="_blank">http://www.mail-archive.com/legacyusergroup@legacyusers.com/...)

Brian from Legacy's support team has responded "The auto complete you are seeing is part of the MS Access database system. It is not something that we can control. That is why it cannot be turned off."

Regards,
Wendy