iCloud Contacts duplicates first name
I list my family and close friends by their first names only in my Contacts, leaving the surname field blank.
Contacts has now started to duplicate their first names into the surname field, so that my wife's entry reads "Fiona Fiona" and my daughter's entry is "Sophie Sophie".
No matter how many times I change the entry, either on my iPhone or on my Air, the first name keeps appearing in the surname field too.
Is Contacts unable to deal with entries containing only a first name?
Has anyone else experienced this?
MacBook Air, OS X Mountain Lion (10.8.2)