From v5.1.0, HTML Export generates files in UTF-8 format including a BOM (Byte Order Marker). The BOM enables web browsers and other applications to more easily ascertain that the files data is UTF-8 and thus to display content accordingly. accordingly, use for the utf8() action is deprecated.
From v5.5.0 the BOM is no longer written. Though a BOM is supposedly the correct standards approach few apps have adopted it correctly. In fact it transpires the presence of BOM causes trouble for all sorts of HTML related tools, so it has been removed from the export process.