I have an example of how to get around this problem in the Liferay Portal distribution. It uses JBoss+Jetty and precompiles all the JSPs and uses some ant tasks to make life easier.
Check it out at www.liferay.com
I suspect that Jboss is not maintaining the original timestamp on files as it is unpacking them - I will investigate when I have time.
Why do you think that precompilation during your development and testing cycle is a bad idea - If I suggested shipping all your servlet and web-service code as '.java's and compiling them on the fly the first time they were hit, would that sound like a good idea ? - just because Jasper has a neat trick to save development time does not mean you should use it all the time.
Have you a particular reason ?