Why doesn't \mkbibbold work while \textbf does when using the ebook package?

Question

To activate the ebook package, one has to put \usepackage{ebook} in the preamble, and \ebook in the document. If both are activated, \mkbibbold stops working while \textbf works fine. Why is that?

I use XeLaTeX -> Biber-> XeLaTeX.

WME

\documentclass{report}
%\usepackage{ebook}
\usepackage[style=authortitle,url=false]{biblatex}
\addbibresource{Qu.bib}

\renewcommand*{\newunitpunct}{\addspace\bibrangedash\space}
\DeclareFieldFormat*{title}{\mkbibbold{#1}}

\begin{document}
%\ebook
\textbf{Bold text} \textit{Italic text}
\nocite{*}
\printbibliography[heading=subbibliography,keyword=Projective geometry,title=Hình học xạ ảnh]
\end{document} 

Results

Log file

If \renewcommand{\bibfont}{\textnormal} is used, then the heading is not large anymore

^{FYI: How to have a bibliography style like Google Scholar?}

Answer 1

The package ebook does not change fonts in a good way. In particular, the result is a different set of fonts is being used in the bibliography. To work around this you can either compile with pdflatex or use

\renewcommand{\bibfont}{\textnormal}

\documentclass{report}

\usepackage{ebook}
\usepackage[style=authortitle,url=false]{biblatex}
\addbibresource{Qu.bib}

\renewcommand*{\newunitpunct}{\addspace\bibrangedash\space}
\DeclareFieldFormat*{title}{\mkbibbold{#1}}
\renewcommand{\bibfont}{\textnormal}

\begin{document}
\ebook
\textbf{Bold text} \textit{Italic text}
\nocite{*}
\printbibliography
\end{document}

with Qu.bib

@Book{Douglas:Moebius,
  author =   {Douglas, Arnold},
  title =    {Moebius transform},
  year =     2000
}