The method WebappClassLoader.validate blocks out the loading of any classes belonging to javax.xml.* package in the webapps/lib and webapp/classes directory. This makes it impossible for a specific web application to use its own XML classes. Also, it makes it impossible for applications to do XSL transformation using javax.xml.transform.* classes. (We are using xalan for this). The work around would be putting the jar files in common/lib, but this is not ideal and prevents each webapp from having its own XML handling classes.
*** This bug has been marked as a duplicate of 6374 ***