1. You can make sure that your setup is working correctly by runnign with "sticky" session with web access only.
2. Upgrade to 4.0.3. I remember I have fixed the mod_jk fail over problem in later release (not sure exactly which one though).
Thank you for the feedback. The clustered config. is functioning quite fine. It turned out(after comparing the 2 nodes' config. files) that the problem was caused by misspelled attribute "jvmRoute"...and obviously there were no session ID sufixes generated from that node.
Anyway, I will follow your advice and upgrade to 4.0.3