AnFI - from your own source document
An observer turning with the tip path plane would see the feathering action changing the pitch of a given blade sinusoidally about the collective pitch setting at one cycle per revolution but as he is turning in the tip path plane he would not see any flapping (except for harmonics).
then
An observer turning with the control axis in forward flight would note that the pitch of the blades was constant, but that the blades flapped up at the advancing side of the nose of the machine and down at the retreating side.
and finally
There is an exact equivalence between the degree of flapping seen by an observer on the control axis and the degree of feathering seen by an observer on the tip path axis. Figure 4.3(c) (not available in the preview) shows that when the control and tip path axes differ by θ degrees, if the blades reach a peak feathering angle of θ degrees with respect to the tip path axis, they will flap to a peak deflection of θ degrees with respect to the control axis.
The reason for the difference between the tip path axis and the control axis should now be clear. In the hover, there would be no permanent difference as the blades follow the cyclic stick. However, in translational flight, the blades encounter highly asymmetrical conditions that pull the tip path axis away from the control axis.
He goes on to say that confusion arises when the axes are mixed which is where I think you are having a problem accepting flapping
PS I think you have made up 'hub axis' and think you mean 'shaft axis' - read your source again!