ProxyPass - error not passed to client

[zoranl]

I know this may be an off topic, but I'm running out of ideas and other forums and maybe some user other from Isomorphic can help me.

I have two ProxyPass directives:

ProxyPass /client/ http://10.0.0.8:8080/client/
<Location /client/>
RequestHeader edit X-GWT-Module-Base ^(.*)/client/(.*)$ $1/client/$2
</Location>

ProxyPass / http://10.0.0.8:8080/client/
<Location />
RequestHeader edit X-GWT-Module-Base ^(.*)/(.*)$ $1/client/$2
</Location>
10.0.0.8 is running Glassfish on port 8080 and http://10.0.0.8:8080/client/ is URL to a GWT based application. Both proxy's work OK ,except when it comes to an error on the Glassfish side. If I go via /cllient/ proxy then I see the actual error that was produced on the Glassfish side. If I go via / proxy then I only see "Error 500 The call failed on the server, please see server log". I've tried settingProxyErrorOverride Off, but it didn't help.

Why don't I see the error via / proxy? I think that the X-GWT-Module-Base header gets edited wrong. This apache configuration is done by https://code.google.com/p/google-web-toolkit/issues/detail?id=4817#c4