Doc type field value not fetched in child table field

I have a Link field “Project” in Material Request docType (parent). A link field with the same name is used in the “Items” child table of the Material Request docType.

Scenario is like:
Select “P1” for “Project” Field and
Select “C1” for “Cost Centre” field of Material Request Form.

Now while inserting first row/item, both field fetches and populates data from parent and displays the same value as “P1” for Project field and “C1” for Cost Center field in Item Child table pop-up.

But while inserting the second row, it does not fetches the “Project” field value from parent to child, while same is happeining for “Cost Center” field.

What could be the resaon for such behaviour. My ultimate goal is to make it auto-populate/copy values of fields in parent form to the fields in child form.