Yes. The field at the top of your screen references the first of many related records--which is the same record as the first record in your portal.
If you are attempting to select a flavor once and have it modify the flavor selection for all the records in your portal, you'll need to do this differently. One option would be to apply your previous lesson (the yes/no field) in reverse and define the flavor field in Delivery Record.
Another option would be to make the field shown in the top of your screen a global field and use a script to update the flavor values in each of the portal records.