[metapost] a problem of label when using metapost

[Source Liu]

Hi,all 

  I've recently figure out something, 
  I sometimes include the package {amsmath} here
as 
====================
     verbatimtex
     \documentclass{article}
     \usepackage{amsmath}
     \begin{document}
     etex 
*some metapost here* 
      
verbatimtex 
\end{document}
etex
====================

I find the latex alway give "failed to generate *mpx" file, 
---> tex --parse-first-line --interaction=nostopmode mp030238.tex
and it gave an error indicate at after btex

I comment the amsmath package, and it pass the compile just fine.


This might be the issue bothered me serveral days ago. I've recently read some history file of the latex and ams team, it does enlight me to look into it. 
:) 

Thanks all, you are all so kind, and helps a lot