I am running existenz 7.0 but I have the same issues with existenz 6.5 or 6.6. or corresponding stock rom. I cannot remember having this issue before this version(existenz 6.0).
I have a sony smartwatch 2 paired all day long via bluetooth. No single issue during the day. I also have a car with bluetooth connectivity. I have issues with my phone (and not with other phones): bluetooth is randomly restarting and sometimes the phone itself reboots.
As it does not seems to be a rom related bug, and bluetooth is working fine with other devices (headset, watch) I think this could be application related. I have some crash dumps, but I am not able to find by myself where the issue could be located. Any help would be appreciated!
Here is a sample of last_kmsg when phone reboots: http://pastebin.com/4j6AX5mu
Sony Xperia Z - Free Mobile
Motorola XOOM Wifi