Problem with GWT behind a reverse proxy - either nginx or apache

I originally asked this question on SO, but perhaps SF is a better place for traction on this question.

I'm having this problem with GWT when it's behind a reverse proxy. The backend app is deployed within a context - let's call it /context.

The GWT app works fine when I hit it directly:

http://host:8080/context/

I can configure a reverse proxy in front it it. Here's my nginx example:

upstream backend {
    server 127.0.0.1:8080;
}

...

location / {
   proxy_pass        http://backend/context/;
}

But, when I run through the reverse proxy, GWT gets confused, saying:

2009-10-04 14:05:41.140:/:WARN:  Login: ERROR: The serialization policy file '/C7F5ECA5E3C10B453290DE47D3BE0F0E.gwt.rpc' was not found; did you forget to include it in this deployment?
2009-10-04 14:05:41.140:/:WARN:  Login: WARNING: Failed to get the SerializationPolicy 'C7F5ECA5E3C10B453290DE47D3BE0F0E' for module 'https://hostname:444/'; a legacy, 1.3.3 compatible, serialization policy will be used.  You may experience SerializationExceptions as a result.
2009-10-04 14:05:41.292:/:WARN:  StoryService: ERROR: The serialization policy file '/0445C2D48AEF2FB8CB70C4D4A7849D88.gwt.rpc' was not found; did you forget to include it in this deployment?
2009-10-04 14:05:41.292:/:WARN:  StoryService: WARNING: Failed to get the SerializationPolicy '0445C2D48AEF2FB8CB70C4D4A7849D88' for module 'https://hostname:444/'; a legacy, 1.3.3 compatible, serialization policy will be used.  You may experience SerializationExceptions as a result.

In other words, GWT isn't getting the word that it needs to prepend /context/ then look for C7F5ECA5E3C10B453290DE47D3BE0F0E.gwt.rpc, but only when the request comes throught proxy. A workaround is to add the context to the url for the web site:

location /context/ {
    proxy_pass        http://backend/context/;
}

but that means the context is now part of the url that the user sees, and that's ugly.

Anybody know how to make GWT happy in this case?

Software versions:
GWT - 1.7.0 (same problem with 1.7.1)
Jetty - 6.1.21 (but the same problem existed under tomcat)
nginx - 0.7.62 (same problem under apache 2.x)

My suspicion is that perhaps GWT is picking up on the Referer header, and getting confused (is there a way for nginx to turn off that header?) or that there's a difference since the traffic between the proxy and GWT/Jetty is HTTP/1.0 instead of HTTP/1.1.