This gets stranger still...
To deploy in a way that works I find I need to add /ServletName/* However, this is not what I want. I then tried /* which is more like the total filter that I want BUT seems to occasionally bring the entire JBOSS server down with out cleaning up after it (no shutting down message just VM exits!) which I wouldn't have thought possible!!!
I'll now try if I can get this to happen in a small easily reproducible form.
OK. It seems that it's a tomcat problem. Trying to use the request dispatcher to include a jsp was causing a circular reference. This quickly blew up the VM. Is there a way for includes to avoid going through the main mapping which causes the servlet to be invoked again for the include? I can use a servlet name but that leaves some files accessible - I was everything to go through the servlet.