As @chris has now confirmed “multi channel association” to be at the core of this issue, I tried reading up on it a little. Being a ZWave newbie, I must admit that I currently do not really understand the background of this problem. In case others are following this thread, are in the same position and are wondering why this stuff doesn’t just work, here are some links that helped me in appreciating the complexity of what Chris is dealing with:
The basics: http://www.vesternet.com/knowledgebase/technical/kb-86
LifeLine, Notification Events & Encapsulation: http://forum.z-wavepublic.com/t/lifeline-and-notification-events/40
Evolving standards: https://github.com/OpenZWave/open-zwave/issues/976