If you delete a contact from the Address Book of a computer or device and then also modify the same contact on another computer or device, the contact may not be deleted after syncing. iSync won't give you any alert message about the conflict.
If you want to delete a contact, avoid modifying the same contact on other devices before performing the sync. If you did but the contact hasn't been deleted, delete the contact and sync again.
Use care when deleting a contact. Be sure to back up your contacts so that if you inadvertently delete a contact, you can easily recover it. See "Working with vCards" and "Backing up Address Book" for more information.