Beats me. I suspect there may be something wrong with the framework’s bridge file. I came across it by running:
current application's ABPerson's |properties|()
--> {AIMInstant, BirthdayComponents, ABDateComponents, MaidenName, Birthday, ICQInstant, FirstPhonetic, MiddlePhonetic, calendarURIs, Suffix, com.apple.carddavvcf, LastPhonetic, UID, MSNInstant, JobTitle, HomePage, InstantMessage, YahooInstant, com.apple.collectionpath, First, Middle, JabberInstant, com.apple.etag, Modification, Nickname, ABRelatedNames, Title, Address, Phone, Organization, ABDepartment, com.apple.synced, Creation, Note, Email, Last, SocialProfile, ABPersonFlags, RemoteLocation, com.apple.vcardhash, com.apple.uuid, ABDate, com.apple.addlInfo, URLs}