Content-Length missing from HEAD request response

Just upgraded to Rails 3 from 2.x. I've got a download method which
returns a file for download via XSendfile. In Rails 2.x a HEAD
request of the download resulted in a response which included
Content-Length, ETag and Last-Modified headers, but in Rails 3 I'm not
longer getting these. Reading the HTTP spec, these should be there.
Any idea what's going wrong and how to fix it?

I'm running with Passenger. And my other rails 2 apps with the same
method continue to provide the missing headers.

Thanks.

Still wondering about this. Any ideas?