Tipping forwards on take-off

My Iris has always seemed to have a tendency to tip onto its nose at take-off.
I have my GoPro Hero3+ Black in a case on the front and have selected the Iris with Front GoPro parameter file in APM 2.0 on my Macbook.
I had the “hotfix” kit from 3DR and did a compass calibration, RC calibration, ESC calibration and gyro calibration. The HUD appears to be responding as expected.
I am running ArduCopter 3.1.5 with the V hull.
If I try and take-off in Stabilize - instant nose dive forwards.
If I try Alt-Hold it just about makes it off the ground, although still tipping forward, but is incredibly unstable in the air - to the point of nose diving into the ground - thankfully long grass, so no damage… yet.

Any ideas what is wrong with my Iris?

Please post a log file.

Here is the log from the latest crash which broke a prop.

I started off in Loiter mode in the hope it would be more stable and it just flew off nose down before tipping upside down into the ground and breaking the prop in the process.

It was never what I would consider to be stable.

I did try using the latest APM 2.0.13 and checked 3.1.5 firmware before recalibrating gyros and compass.