I was actually previously 1 build behind the latest, so in the end, after restoring my previous state, I did another dirty flash. and just did a quick test, and I was able to hang up with my headphones on. Its possible that a call recorder app I had installed (which defaulted to recording every cal) may of been related / a cause. I tripped over the dest directory and then realized it had been automatically recording every call. I have now also turned that off. Sorry for any trouble, from now, I'll wait until I can duplicate any issue on a clean flash.