[XeTeX] problem with addfontfeatures and lm-default

[Stefan Solbrig]

Dear all,
I have a minor problem using fontspec.sty.
The following miminal example produces an error when
compiled with
xelatex -output-driver=xdvipdfmx

\documentclass[12pt,a4paper]{article}
\usepackage[lm-default]{fontspec}
\usepackage{xunicode}
\usepackage{xltxtra}
\begin{document}
\addfontfeatures{Mapping=tex-text}
some text
\end{document}


The error I get is:

! Missing \endcsname inserted.
<to be read again>
                   \zf at family@optionslmr
l.7 \addfontfeatures{Mapping=tex-text}

I'm using xelatex version 0.996  (as included in texlive 2007)
and fontspec.sty v1.13 (also as included in texlive 2007),
both on OS X

I traced the error message to line 128 in fontspec.sty, but from there
on, I don't know how to proceed.
It's not an urgent problem, but it would be nice in order to typeset legacy
TeX text  by default e.g., with  `` denoting left quotation marks.

However, it works perfect if I load the Latin Modern fonts
via fontspec by hand:

\documentclass[12pt,a4paper]{article}
\usepackage[lm-default]{fontspec}
\usepackage{xunicode}
\usepackage{xltxtra}
\begin{document}
\fontspec{LMRoman12 Regular}
\addfontfeatures{Mapping=tex-text}
some ``legacy'' tex-text
\end{document}

Thanks!
Stefan