Doesn't appear to be COS related... I opened a ticket with Mitel and their was basically "Yeah, we know"... what they actually said was "Upgrade, there are several DPARs since this revision that relate to Call Forward Profiles, especially in clustered environments, and that should correct your issues since the rest of your configuration looks correct" but at this time we can't upgrade any further than 4.2 due to incompatibilities with their 6510 voicemail, once that is upgraded later this year we will be able to upgrade to the current release. So the answer is just use FACs for now... well, the customer accepted that so I guess I am OK with it.