Been retired for several years now, but I remember the IAS and Mach increasing in chop, and having to pull some power off. I reached the point where, as soon as we hit a little chop, I'd wind the speed back a little, in order to anticipate the increase. But I never knew the reason for this phenomenon.
The other little 777 'nasty' was its habit of pitching down quite severely if the speedbrakes were deployed without finesse.
Nice piece of kit, though. Be interested to see if there are any aerodynamicists out there with an answer.