That is intentional, and handled by the Flight Engineer to limit the amount of turbulence off the blades affecting the closely following wing, for better ride quality.
Seeing there were some comments earlier re the L188, it was a little different in that the props - quite slowly - rotate when feathered (too long ago to recall the reason) .. felt like going over a road speed hump .. at speed .. each time a blade crossed the LE .. those were wonderful days ...