I had built the quadcopter like what you had done but I had a problem, it keep spinning clockwise went trying to flying up. This happened is because two motors were stopped. From the multiwiiconf, I saw the motor speed was below the min throttle of the ESC. I had calibrated the ESC too and No bad connections.
The only difference was I am using the code from github. Is that the reason? I am eagerly wanted to finish this project.