I live in central Florida. Our horizons are as flat and level as water. Yet, when I rotate, this is what I get:
I've found that the delay in adjusting for yaw on the camera is too slow when flying in wind. If wind is pushing from the right, for example, the right side of the MP will be slightly lower as it compensates for the push. Rotating (yawing) the aircraft in such conditions means the bird is not only spinning, but as the opposite side of the aircraft faces into the wind, the airframe has to lower the opposite side. That 'wobble' happens too fast for the yaw axis of the gimbal to properly compensate. When there is no wind at all, the same spinning produces no changes in horizon tilt.