[XeTeX] \XeTeXmathcode problem with amssymb

[Mehdi Omidali]

Hi,
I compiled the following lines with xelatex (0.998.3) on miktex 2.7 

\documentclass{article}
\usepackage{amssymb}
\font\tenrgm="Scheherazade" at 15pt
\font\sevrgm="Scheherazade" at 9pt
\font\fivrgm="Scheherazade" at 7pt
\newfam\fardig
\textfont\fardig=\tenrgm
\scriptfont\fardig=\sevrgm
\scriptscriptfont\fardig=\fivrgm
\XeTeXmathcode`2="7 "4 "06F2%
\begin{document}
$$2x^2$$
\end{document}

and the result is http://www.omidali.com/sample1.pdf
The problem as you see is that the numbers 2 (and any other number) is not
shown. But if you just commnet \usepackage{amssymb} it works perfectly like here
http://www.omidali.com/sample2.pdf

Is this again just a miktex problem?