[XeTeX] Isomath, Mathspec and Siunitx

[Le Farfadet Spatial]

Hello everybody out there!

     I am experiencing some troubles while using together Isomath, 
Mathspec and Siunitx. First, it seems that the font Linux Libertine does 
not have any bold italic characters. As a consequence, when using 
"\mathbfit" in mathematical environment, the font is not Linux 
Libertine, but LModern. LModern is also used with predefine function 
such as "\ln", and with Siunitx. Here is an example summarizing the 
troubles I have:

\documentclass{article}

\usepackage{isomath}
\usepackage{mathspec}
\usepackage{siunitx}

\defaultfontfeatures{Scale=MatchLowercase}
\setromanfont[Mapping=tex-text]{Linux Libertine O}
\setsansfont[Mapping= tex-text]{DejaVu Sans}
\setmonofont{DejaVu Sans Mono}
\setmathfont{Linux Libertine O}
\setmathsfont(Digits,Latin)[Numbers={Lining, Proportional}]{Linux
Libertine O}

\begin{document}
\sisetup{group-four-digits=true, output-decimal-marker={,},
    exponent-product = \cdot, detect-all, detect-inline-family=text,
    detect-inline-weight=text, detect-display-math=true}

\SI{6}{\meter \per \second} $\SI{6}{\meter \per \second}$

\emph{\bf u} $\mathbfit{u}$ $\mathbfit{\tau}$

ln $\ln$
\end{document}


     I do not know if anybody has an idea to fix these.

     Regards.

                                                     Yoann

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