Queries :: Why Is Data Being Deleted

I have the following set up:A table in access for PurchaseOrders

-A table in access for ShipmentDetails, PK linked to PurchaseOrders OrderNumber
-A table in access for payments, an index linked to the PurchaseOrders OrderNumber
-An SQL database table of purchase order details from our existing system, linked to PurchaseOrders OrderNumber

Now, I create a new record in PurchaseOrders with OrderNumber="ABCD01". All good.I create a new record in ShipmentDetails with OrderRef= "ABCD01". Still good, creating a form and adding fields shows the data is linked correctly.

I now add the CreditorCode field from the linked SQL DB, it automatically shows like it should.I try to use the form to delete the "ABCD01" record from the PurchaseOrders table and it deletes the record FROM THE SQL DATABASE! It's basically acting like Enforce Referential Integrity is turned on with deletes. This backend DB is used by other programs. I don't ever want my app to modify it.