Currently, under Tomcat under JBoss does not provide a way in which to prevent deletion/cleanup of the temporary files created, including the .java and .class files derived from the JSP. I do not believe the DeleteWorkingDir is processed in any meaningful way.
You can enable debug for server.log and observe the output to see whether it processes the tag. You will probably find it has no discernible or recognised action for the tag.
There has been a method suggested in the forum to configure Jasper to generate the temporary files in a separate directory. It is a bit messy.
Jetty has a configuration setting that allows a temporary directory to be specified on a per WAR basis. It is also described in the forum.