Importing AP Invoices-problem with duplicate invoices

SUGGESTED

We have been importing AP invoices for years, using the AP Utilites>AP Import.  We recently discovered that the same file can be imported again after the file has already completely posted in AP.    The exact same file was used, so the Vendor ID and Invoice Number did not change in any way from the first import.  We have the AP setting to Warn for duplicate invoices, so my question is, does the AP Import bypass that safeguard?  Should we be using the Data Import instead?

We are on version 7.4 June 2012 update of Sage 500 ERP.

Any help would be greatly appreciated.