Yutaka Emura

You can disable the Auto Detect result dialog box:

Select Customize on the Tools menu, select the File tab, uncheck Always Show Detect All Result check box.

By default this is checked because the Auto Detection can make mistakes sometimes especially in small files. But if that is not a problem, you can uncheck this option. If you see a mistake, you can always reload the file as a correct encoding by double-clicking the encoding on the status bar.