Why is Babel intefering with xypic here?

Question

This file runs fine if I comment out the usepackage brazil line.

\documentclass{amsart}
\usepackage[brazil]{babel}
\usepackage{xy}
\input xy 
\begin{document}
\[\xy  ,(0,0)="A" \endxy   \]
\end{document}

But if I do not comment it out I get an error message and no pdf:

! Paragraph ended before saveid@COORDi was complete
<to be read again>

Can someone tell me why it is happening?

I need to have the babel brazil, and I hope I can use my actual (much longer, of course) xypic with no major changes.