Select View|Options... and then make sure that the check box labelled 'Hide MS-DOS file extensions' is unchecked.
Select View(or Tools)|Folder Options... then select the View tab and make sure that the check box labelled 'Hide file extensions for known file types' is unchecked.
After changing this settting, you can then see the real full file name and change it if necessary. To avoid the misnaming of files when saving them, the file name can be placed between double quotes, for example, "berks.bdy". Remember also that versions of DMAP before V7.0 do not accept long file names, so the file name must consist of a maximum of 8 characters for the name and a maximum of 3 characters for the extension.