I should have mentioned, compiled from scratch with the apache sources.
JBoss is included as part of a larger proprietary application so upgrading it cannot be done without the vendor (HP).
The current version of mod_jk I have does work fine....
I attempted using the new mod_jk with Tomcat 5.5.20 and it works fine.
I'm assuming its a really old bug in an old version of JBoss, or the newer mod_jk is too new for the old jboss.
Anyway, if anyone else has this issue hopefully they won't lose too much time with trying to solve this.