PHP set header location without outputting HTML

I am creating a RESTful API in PHP, and have encountered a problem with the location header.

I want to return 201 Created, with some XML data, and a Location header.
When I set the location header in PHP, IIS automatically changes content-type to text/html, and adds a little text on top of my XML.

Related question, with code that produces the problem:
http://stackoverflow.com/questions/12074730/php-set-header-location-without-outputting-html/12074890
(I am the poster)

I am runnning PHP in FastCGI on IIS 7.5 on Windows 7 Proffesional.

Any solutions?