HTML pages returned as plaintext, who is the culprit?

I have been moving applications from my Rackspace host over to Amazon’s EC2 service.  Moving simple LAMP apps has been fairly cut and dry, but while moving a RoR app and accessing it through apache w/ mod_proxy, the html is delivered to the browser as plaintext.  If I access the app directly on mongrel’s port, it renders correctly.   So it appears that something with either my mod_proxy configuration, or something about how my EC2 instance is set up is causing the problem.


> curl -I http://linux.local:3000
HTTP/1.1 200 OK
Connection: close
Date: Thu, 15 Jul 2010 14:27:27 GMT
Content-Length: 0

> curl -I http://linux.local
HTTP/1.1 200 OK
Date: Thu, 15 Jul 2010 14:27:35 GMT
Via: 1.1 linux.local
Content-Type: text/plain


As you can see, when accessing the page through Apache/mod_proxy, the Content-Type that is returned is explicitly set as text/plain.

Update
This is a bit shoe-horned, but it works for right now. In the apache2.conf file, I changed the DefaultType from text/plain to text/html. The reason this solution “concerns” me is that on my other servers, (where this problem is not occurring) the DefaultType is also set to text/plain, but the html is output correctly.