Invisible math characters with unicode-math and ntheorem

Question

When compiling this code with lualaTeX (from TeXLive 2011),

\documentclass{minimal}
\usepackage{unicode-math}
\usepackage{ntheorem,thmtools}
\setmathfont{xits-math}
\makeatletter
\newtheoremstyle{mathfonttest}
  {\item[\theorem@headerfont $ABC$ DEF $:!?$ ]} % 1. option
  {\item[$ABC$ DEF ]} % 2. option
 \makeatother
\declaretheorem[style=mathfonttest]{test}

\begin{document}
\begin{test} % 1. option, ABC invisible
  Something. 
\end{test}
\begin{test}[triggers 2. option] % 2. option, ABC visible
  Something.
\end{test}
\end{document}

the first ABC, and more generally any greek or latin character in inline math mode – when preceded by \theorem@headerfont – is invisible and I have no clue why. What I want to do is use math code in optional or alternative description to a definition like '1.1. Definition (of $pi$)'.

Does anybody know how to solve this or circumvent it?

Answer 1

The problem is that \theorem@headerfont calls \theorem@checkbold and this macro does

\if b\expandafter\@car\f@series\@nil\boldmath\fi

This is the reason for the disappearance: the font used is boldface and this causes \boldmath to come into action but XITS Math has no bold version.

If you want to use ntheorem and math in the theorem labels, then you need to use a non boldface font.

The most recent TeX distributions (TeX Live 2012) should have a bold version of XITS Math, so you can try updating yours.