For your own safety, the manually deleted contact fields (single phone number, addresses,...) e.g. in the source app are not also deleted in the target app.
This is the only way sync.blue® ensures even more data security, as accidentally manually deleted data is still preserved in the other apps.
Tip: instead of deleting a value of a contact field completely, replace it with, e.g. "-" so that it will also be synchronized in other apps.