How does the iSync connector find conflicts? For the fun of it, I have set up the sync to "Manually" on my Mac, I modified a email address of a contact, and I did the same thing on my iPhone (same contact, but different email address). After done that, I launched a manual sync on my Mac, and the contact's email address from my Mac was updated to ZCS (and my iPhone). I did the same steps a second time, and this time, the contact on my Mac was updated with the one coming from my iPhone! So not only I wasn't told that a conflict was there, but the behavior was different :-/
Enabling "Show data change alert" didn't change anything.