Ah, so that's the convention.

Supposing foreign postal codes are entered in a different field than the one for Zip Code, my hunch is that it's programmed to omit the Zip, have it as 00000 or 99999, or it just goes wonky without the required input (which then causes the file to get locked up without a usable password).

@Ashley at Intuit (aka Henry Jr) Could you please confirm?  Thanks!