[texhax] LaTeX hangs up with $(\ref{label})$ and [spanish]{babel}

[Juan Ignacio Montijano]

I have experienced an annoying behaviour of LaTeX.  When I use a reference 
inside math mode
the TeX program hungs up without any error message.  I have reproduced the 
problem in the small document below.
This happens when using  \usepackage[spanish]{babel} and after using \chapter.

I am using MiKTeX 2.2

Is this a bug ?
It is not a problem, but if you do not know the reason why the program 
hungs up you cal lose quite a lot of time.

======================
\documentclass{book}
\usepackage[spanish]{babel}
\begin{document}
\chapter{Chapter}
\begin{equation}\label{label1}
a=b+c
\end{equation}
Using the reference $(\ref{label1})$

\end{document}
=============================


Juan I. Montijano              e-mail:  monti at unizar.es
Dept. Matematica Aplicada      Tf.:     +34 976 761120
Universidad de Zaragoza        FAX      +34 976 761125
50009-Zaragoza (Spain)