problem syncing yahoo contacts

[robbonds]

my wife and i both have iphones - we use the same itunes account because thats where all OUR music is
we both have our own yahoo email accounts and different contacts
when we sync our iphones to itunes and select yahoo (we configure for our individual yahoo accounts with passwords) som how our yahoo contacts get merged - contacts from both accounts show up on iphone...also - when i look in my contacts on yahoo all my wife's contacts show up too

please help
thanks
love my iphone