Saving as Html leaves question marks in place of certain characters

When I do a document.Save(stream, SaveFormat.Html) (Aspose.Words) certain characters get replaced with question marks. One example is the £ sign being replaced as ?. Others are word smart quotes.
I have tried explicitly setting the SaveOptions.HtmlExportEncoding = Encoding.UTF8 (and others) but to no avail.
Any ideas greatly appreciated.

Hello

Thanks for your request. Could you please attach your document and provide me sample code, which will allow me to reproduce this problem? I will check the problem on my side and provide you more information.
Best regards,