I have used mission planner to evaluate the logs and get an idea as to why my quad decided to abandon me and fly away. Posn hold fm.
At the time the quad just started showings signs of its independence the data table showed for the imu line eg and ea change from zero to one. This can also be viewed by selecting imu menu on the right hand side of the screen (MP) and clicking on imu then eg and or ea.
What does eg and ea stand for? What is their source in the github code. Appears it ends up as a logic command that does something bad.
Have you read this?
http://ardupilot.org/copter/docs/common-diagnosing-problems-using-logs.html#vibrations
Also, if you read other posts similar to yours, the usual advice is that you post the *.bin file from your data log.
So you might want to try that