tidy shouldn't parse a php file text/css

Hi

I've installed Tidy, i have in my apache config:
AddOutputFilterByType   TIDY    text/html

So it should process only text/html files, however i have a simple php script that does this:
<?php
  header("Content-Type: text/css");

  echo "some css...";
?>

And this file is also processed by tidy, but it shouldn't

Any idea how i can fix that ?
Every trick is welcome (force type on certain files, force tidy not to execute on certain files, etc...)

I've tried many things, i don't find... 
Maybe someone of you has a work around

Thanks
Enzo