I see a lot of saves work like this:

    f = open( "the_file.new.$$" );
    write( f, new_contents );
    close( f );
    rename( "the_file.new.$$", "the_file.new" )

If not implemented like this, then something that attempts to read "the_file.new" may get partial contents, normally truncated along the file system block size.

Backups often take place, too, like you mentioned, depending on editor.