Configurable Form - Default Segment Values

Summary:

When defining a segment for a configurable form on a Journey task. I am using a table validated valueset for a list of employees which works fine. However, when I add SQL for a default value nothing is shown and the field is blank until the record is saved and then it appears. We want it populated when you open the form.
It seems to be something with the ID Column Name. I created a test with a character attribute column, valueset returning the last_name only and no value for ID Column, and a simple SQL statement for the default value returning the last_name and it works fine (shows on form entry). But obviously it saves the last_name into the database which is not what we want. We want the person_id saved into the attribute column in the database so any name changes are reflected correctly.