In Application mode, the import or export dialogs work with the virtual structure of 4D.
If there are fields marked as invisible you will not see them in the import/export dialogs.
If you renamed the fields with SET FIELD TITLES you'll get the virtual name in the import/export dialogs..

In Design mode, when you use the File/Export or File/import menu options you're in design mode and working within the real stucture so the fields are visible and using their real names.