He's probably been frustrated with the company since Scalebound, this was only a matter of time. Everyone knows Kamiya isn't exactly shy about sharing his opinions so I bet he's been butting heads with people nonstop. Hope he pulls a Kojima and gets some funding to do his own thing.
Oh wow Scalebound, I was so excited for that game. Wish he was able to finish that as he seemed to be very passionate towards it. I heard MS was extremely pissed with the development process as well.