Well, here's what seems to be happening. The camera cannot track the plane in fast movements. That's because the inertia system allows the aircraft to shift from the centre of image in normal flight. However, the system cannot adapt to fast changes in the aircraft's attitude.
This is most evident in spins, but very fast turns in some biplane might also trigger this. As the aircraft is spinning, the inertial system makes the viewpoint "lag behind" and the panning component doesn't move the camera quite fast enough to keep aircraft in view, and you end up seeing empty sky most of the time.
I'm not sure what should be done about it. My intuition tells me that either the camera needs to be able to pan faster (to keep the target aircraft in sight at more severe maneuvers), or alternatively the inertial shift of camera view point relative to the aircraft needs to be constrained.
It would be ideal if it were possible to make the camera able to pan faster when required, when the target aircraft keeps moving off-centre faster. I'm not sure how this could be done - perhaps some sort of "ramp-up" to maximum panning speed? That way, the camera would react slowly to small maneuvers and you would be able to keep the wonderful "bobbing" camera motion in normal flight, but once the camera is moving longer, it would reach a higher panning speed, being able to track the aircraft in the view more effectively.
Again, though, since I have no exact idea how the code is structured, these are just suggestions based on the behaviour I can see, and my interpretations of what might be going on under the hood.