Indeed, this is a peculiar bug. The offline demos have been saved in a different encoding, so the UTF BOM gets visible when using the editor. The online demos are served with the proper content-type, so they are fine. You can resolve this in the offline demos by specifying the following meta tag:
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
(note that there are subtle differences and specifying <meta charset="utf-8"> won't work)
In any case, this problem does not appear when the encoding is correctly set, so it shouldn't hinder your evaluation.
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