Why is the locator field behavior different in an editable query?

We have an editable query section, where a locator field is one of the editable columns. This locator field has a query to list only associated records. When we edit the locator field from the query section, it lists all the records (not only the associated records) from the BO. But if we open the line item and edit the locator field within the record, it lists only the associated records to select. Can someone explain why there is a difference and is there any way to fix it?