Active char interaction with babel (et al?)

[wspr]

[From Simon Derouault]

With this setup, I can't use the factorial sign (!) in equation. The compilation freezes and no error is given. It is probably related with the special spacing with the exclamation mark in french babel (although it shouldn't concern mathematical environment).

Here is a minimal code to reproduce the bug :

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[francais]{babel}
\usepackage{amsmath}
\usepackage{breqn}
\begin{document}
\begin{equation}
x=5!    
\end{equation}
\end{document}

With english instead of francais in babel option, the compilation run just fine. The same error occurs with breqn environment like dmath. Is there some workaround that I can use ? For now I use !\text{!}, but it's not an elegant solution. Otherwise the breqn package does a marvelous work and saves me a lot of time, I would not do without it !