Why does It only show actual result in portal when after loading related record.

I'm accessing Oracle Database Server via ODBC.

Then I added three tables to FileMaker from Oracle DB.

These tables are related such as below

1. Customer (customer_id)

2. Receipt (customer_id, receipt_id)

3. Item (receipt_id, item_id, item_name)

note: Items belong to Recept, and Receipts belong to Customer.

I built a portal in order to show the detail about when, and what a customer bought by reffering purchase history.

Then here's a question.

I'm on Customer Layout(showing all Customer records)

In spite of the fact that the customer has purchased something before,  nothing appears in portal

It should show the date of purchase, and the name of the item, though!

Another additional weird thing.

If I go to Receipt Layout(showing all Receipt records), and load record(Suppose customer_id="12345678")

then go to Customer Layout and find a customer by customer_id="12345678"

Now, It shows actual result in portal.  Why is that!?

Is it something related to index? Does it automatically add index to a record when after load a record??

Do I need to do something special to show actual result in portal as default?

Any solution?