[XeTeX] bug using \underbrace with unicode-math package

[Daniel Greenhoe]

Using \underbrace with the unicode-math package under XeLaTeX produces
garbage output. Here is a minimal example:

\documentclass{book}
 %\usepackage{mathspec}              % no problem
 \usepackage{unicode-math}           % problem
 %\setmathfont{lmmath-regular.otf} % |{z}
 %\setmathfont{Asana-Math.otf}      % ||{z|}
 \setmathfont{xits-math.otf}              % |{z}
\begin{document}%
  \[ \underbrace{xyz} \]
\end{document}%

Using the mathspec package instead of unicode-math seems to be OK.

The \underbrace with unicode-math problem was discussed almost one year ago:
  http://tug.org/pipermail/xetex/2010-November/019236.html

Anyone have a solution?

Many thanks in advance,
Dan