iframe remoting with remote_upload and responds_to_parent problem

Hi Folks,

I'm trying to upload images with the ajax scaffold plugin using the tutorial
here: http://blog.flornet.fr/magazine/article/2

For some reason, however, whenever I submit my form_remote_upload_tag form (a
non-ajax form with an iframe as the target), I get a 404 error, and no data
is added to my development log. If I just use form_remote_tag, the
ajaxscaffold default, the request at least reaches the server, though of
course I can't upload my file. I'm using mongrel.

I've pasted the requests and their results here: http://pastie.caboo.se/24422