I don't know much about quads but isn't there some sort of balance calibration for the escs to be done before flying?
Could be I manually calibrated each ESC. I have read in the forms to use a hand programmer to make sure they all have the same settings. I have noticed one ESC has breaking turned on while the others do not. I am also wondering if the motors are pulling more power then the battery can give.
The motor can't pull more power than the battery can give. I have had a flip caught on video and posted here http://www.availabilitydesign.com/Downloads/UAVCrash.html - there is more power applied as you can hear but the cause is unknown by me.