Description of problem:

* "ProxyErrorOverride On" does not work if used with mod_proxy_ajp module. When I access a 404 URL in the /app context, which is proxied with AJP, I get a 404 page from backend servers (Tomcat, JBoss EAP, and so on). 
* Accessing 404 URLs via non-proxied content works as intended, as defined in "ErrorDocument". 
* It works in mod_proxy_http (i.e. changing protocol to ajp to http).

[ Config Snippet ]
~~~
ProxyPass /app/  ajp://127.0.0.1:8009/app/
ProxyErrorOverride On
ErrorDocument 404  /error/404.html
~~~

Version-Release number of selected component:

* JBoss EWS 2.0.1 (httpd-2.2.22)


How reproducible:

Everytime.


Steps to Reproduce:

1. Define "ErrorDocument" and enable "ProxyErrorOverride" on mod_proxy_ajp setting. For example:

    ProxyPass /app/  ajp://127.0.0.1:8009/app/
    ProxyErrorOverride On
    ErrorDocument 404  /error/404.html

2. Access a 404 URL via definied "ProxyPass" context

    curl -v http://localhost/app/foobar
  

Actual results:

* 404 error from backend (proxied) server.


Expected results:

* 404 error as defined in "ErrorDocument" via Apache httpd.


Additional info:

* There is an Apache BZ https://issues.apache.org/bugzilla/show_bug.cgi?id=50945 and a fix http://svn.apache.org/viewvc?view=revision&revision=1087864 for this issue in upstream.
* There is a Red Hat BZ#694939 for Apache httpd in RHEL 6. And it has been fixed in Apache httpd rpm package httpd-2.2.15-15 included in RHEL 6.2.