[XeTeX] Getting vinculum in fractions with Asana Math and unicode-math when compiled with xelatex

[R (Chandra) Chandrasekhar]

Dear Folks,

With this minimal example:

---
\documentclass[a4paper,12pt]{article}
\usepackage{fontspec}
\usepackage{unicode-math}
\setmathfont{Asana Math}
\begin{document}
$\frac{2\pi r}{r} = 2\pi$
\end{document
---

I am unable to get the horizontal bar or vinculum for the fraction on 
the left when I compile the file with xelatex, although I can get it 
when compiled with lualatex.

FYI, I am using TeXLive 2010 on Kubuntu 10.04 and the relevant versions are:

XeTeX, Version 3.1415926-2.2-0.9997.4 (TeX Live 2010)

unicode-math.sty    2010/09/27 v0.5b Unicode maths in XeLaTeX and LuaLaTeX

ASsana Math Version 000.928

Can someone please suggest how to compile the file correctly with xelatex?

Many thanks.

Chandra