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Here's the screenshot of what I see when I run the script. (I extracted it to my c:\temp directory.)kesukomu-mojibake2.png
As you may see, there is something before the xcopy command. Not sure how you inserted the BOM signature, but it appears to not get read properly by DOS.
Perfection as a goal is a nice idea that can point one in a specific direction. However, since "perfection" is an ever changing (evolving?) and moving target, one must admit that perfection can never be obtained...
When in doubt, check the d4mn source code!