Why does Supplier SetID default into Search criteria for Voucher Staging Cleanup?

We're in the process of updating to PUM 9.2.36 with PT 8.57.14. As part of this update we're giving users access to the new Voucher Staging Cleanup functionality.

During testing, we're finding that Business Unit is a required field, and once the user enters a Business Unit, the Supplier SetID field is automatically populating based on the Business Unit entered. However, the field VENDOR_ID is not an available field on the ExcelUploadforVouchers spreadsheet and therefore isn't populated in the voucher staging record (VCHR_HDR_STG).

Since the VENDOR_ID field isn't populated in voucher staging records, the user receives a message that No data is found for the given search criteria. If we set the Supplier SetID field to All Values, then the results are returned.