The yaw damping...at least, I assume that's what's causing it, wags the tail in the lightest of chop. On one occasion, my coffee was slopping 3/4" up the sides of my cup, for hours, for no apparent reason.
Yaw damping is helping prevent yaw. I'm sure your tea would be in your lap (or the lap of the person sitting next to you) if it wasn't for this system
Modern yaw damping systems even help counteract the twisting/bending of the fuselage due to crosswinds.
But, having said that, I'd imagine the system has some kind of reaction time. It wouldn't be able to eliminate all the yaw.
Rgds.
NSEU