Okay, okay....I wanted to test this "yaw defect" myself....well, I did find that the higher the altitude, the banking and wobbling occurs at around 36,000 - 40,000 feet...but it can be rectified by applying trim and use "cruise" speed at or slightly below 350 knots...
I have gained on full thrust from 35,000 feet at a 60 degree angle to 50,000 feet (the max for this jet) and returned to normal cruising speed at or about 350 knots...maybe 400 knots with applied trim and found no wobble....
Speed is the factor at high altitude, air is thinner and makes things go "faster" with less stability if it is not designed for high speeds at high altitudes.
I find it not to be a problem, but to correct the issue if it arises....part of logically thinking as a professional pilot.