Either "no harm, no foul", or this is a technique with a desired side effect that I'm unaware of.

file_save_upload() is invoked sequentially with the same arguments (result-checked the 2nd time) from node_import_add_form_submit_upload_file() in node_import.admin.inc

Since I'm using this module as a model, it would be nice if it were either not there or documented, but this is a way minor issue.