Aspose converts empty bullet to “o” letter when using fixedHTML. Please see attached screenshot.
Thanks for your inquiry. Please note that Aspose.Words mimics the same behavior as MS Word does. If you convert your document to html using MS Word, you will get the same output. Moreover, if you change the font name of bullet list to "Calibri", its appearance will be same like "o".
Please let us know if you have any more queries.