Custom Error Pages (404 & 500) not invoked (JSF 1.2 & Websphere 6.0.1)

Question

Hopefully this is very obvious to some of the experts here. I'm trying to have my custom error pages (404 & 500) displayed, but in stead I get the normal system output text (ugly). The web.xml has been configured to apply the FacesServlet to all pages ending with "jspx". What I now get is the following: Whenever a page ending with .jspx cannot be found, the custom 404 page is IGNORED, however, when I don't use .jspx, but .jsp for example, IT WORKS. Below is my web.xml. I have already tried to make the error pages plain html, and also moved them to the root directory, no luck.
Oh yes, running on RAD 6.0.1, Faces 1.2.
Please if someone could guide me here...
########## SNIP ##########
<servlet id="Servlet_1212573625706">
<servlet-name>Faces Servlet</servlet-name>
<servlet-class>
javax.faces.webapp.FacesServlet</servlet-class>
<load-on-startup>-1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>JS Resource Servlet</servlet-name>
<url-pattern>/.ibmjsfres/*</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Faces Servlet</servlet-name>
<url-pattern>*.jspx</url-pattern>
</servlet-mapping>
<error-page>
<error-code>500</error-code>
<location>/includes/errorPages/error500.jspx</location>
</error-page>
<error-page>
<error-code>404</error-code>
<location>/includes/errorPages/error404.jspx</location>
</error-page>
########## SNIP ##########

Answer 1

I recognize this as an appserver bug (yeah, it's Websphere).
Websphere (and the older versions of Apache Tomcat where it is actually based on) doesn't expect the error-page to be a dynamic servlet-served page, but as a static page. It roughly handles as follows: get the error-page location from web.xml, test its existence on the disk file system, if positive then go ahead, but if negative then display default error screen.
The file with .jspx extension does not physically exist on the disk file system. A workaround for which I remember it worked in WAS 5.x is to create physically that file (empty content is allowed) on the disk file system. So create a blank file with jspx extension at the same location.