Looks like do=export_html was at some point renamed to export_xhtml. actions.php has a cute little workaround for that. However, template.php checks whether $ACT=='export_html', which is nonsense, because even if the user would have supplied it that way, it would have been rewritten by actions.php. The <link rel="alternate"> tag template.php outputs for the "Plain HTML" version is wrong as well, although that error is rather cosmetic; it works nevertheless. The $ACT comparison however is really breaking things (<meta> date doesn't get sent, for example) and since fixing this requires just one additional byte in the file, it should be done in the next version. I've even created a patch for that really trivial bug, see attachment.