Cached pages and content negotiation


I seem to be unable to get the server (Apache 2.0.61 with Phusion
Passenger 2.0.3) to return cached non-html pages.
My application caches RDF-XML files in the file system with an .rdf
extension. The URLs to retrieve the data (I'm using ActiveRecords, not
ActiveResources) don't use file extensions, so I am calling
'ActionController::Base.page_cache_extension = ".rdf"' from the
controller. My requests have a header "Accept: application/rdf+xml"
and I've added "AddType application/rdf+xml .rdf" to /
public's .htaccess file.
Albeit the server never returns the cached pages, instead rails sends
a new response.

When I change the file extension of a cached file to .html and use a
browser to request the data, the cached file is returned. So some sort
of content negotiation is at work here, but it only works for html

Any ideas, anybody?