Repost: IE applies transformation, Fx does not

Hi list,
I've a xml file with a PI specified:
<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet href="../view_names.xsl" type="text/xsl"?>
<doc xmlns="http://www.w3.org/1999/xhtml">
...
</doc>
When I invoke a file like this with the browser, the file is fetched,
gets transformed
and the result is displayed, for both Fx 1.5 and IE 6.0 (MSXML 3).
When I fetch the same file via javascript httprequest, then IE applies the
transformation automatically before giving me access to the result-tree,
whereas Fx (also Opera 9.0 beta) gives me the xml input-tree.

Is this difference documented anywhere?
May I prevent that transformation on IE somehow?

Regards, Manfred