well, according to TB manual..........
"If you have stored contacts with the similar contact information such as name, email address, or mobile number in your phone and online accounts, your phone will try to link them as one automatically or create a list of matched contact suggestions. If it doesn?t, you can manually link them so that you won?t have duplicated entries in your contacts list.
Also link your contacts with other social network accounts such as Twitter and Flickr. You?ll then see their updates and events from these accounts all in one place."
I still don't know how to stop the phone from trying to merge/link the contacts by default.