classloader issue with xercesImpl

Hi all,
I'm working on a migration from websphere to Jonas 5.1.6+JDK 1.6. For some
reason, this application is doing :
Class parserClass =  Class.forName("org.apache.xerces.parsers.DOMParser");

Runing this code gives me the following exception:
java.lang.ClassNotFoundException: org.apache.xerces.parsers.DOMParser

I wonder how this is possible, because xercesImpl-2.9.1.jar is in
$JONAS_ROOT/lib/endorsed, so I was expecting that the included DOMParser class
should be available everywhere.

I have this error with java2-delegation-model set to true or false.

I also tried to include xercesImpl-2.9.1.jar in my WEB-INF/lib war folder. This
solves the previous error, but prevents jonas to compile jsps, giving me this
error :
java.lang.ClassCastException:
org.apache.xerces.parsers.XIncludeAwareParserConfiguration incompatible with
org.apache.xerces.xni.parser.XMLParserConfiguration.

How should I solve the ClassNotFoundException mentionned ?

Regards,
Bernard