Trailing Slashes and Reverse Proxy

Hello,

I'm running a reverse proxy using nginx 1.2.8 to a number of apache2 servers sitting on local private IP space. When content using relative links is served, links including a trailing slash work correctly (ie ../../dirname/), whereas links without the trailing slash (ie ../../dirname ) return the private IP address of the proxied server to the end client (eg 10.0.0.101 instead of virtualhostname.host.com). What could be causing this behaviour?

Thanks
macaque