Yes it does. For cheking whatsapp users in your phonebook it needs to send all that data to Whatsapp Inc. servers and it saves all that data and updates it (I supose that every time the program is openned data is resent (so in most mobiles when mobile is rebooted). And that data could be sold. And Whatsapp privacy policy could change without telling about it to the users (wich is ilegal in Spain and maybe in all Europe and other countries). Did you read Whatsapp privacy policy? For me is unaceptable.
Well, then I only have to remove international prefix to the ten contacts I have with it and add it to the contacts I know that have whatsapp. You forgot to reply one of my questions. Will you implement an option to not sync contacts when you implement synchronization? Pleaseee (Showing a nice-guy face. XDDD).