Originally Posted by
Bus Driver Man
It’s even noticeable when selecting open climb: after the engines have already spooled up, selecting a lower speed to increase the climb rate will initially result in a thrust reduction by the A/THR before increasing it back to CLB thrust. Again, I have never seen this on CFM engines.
It most certainly happens with old CFMs too.
Courtesy of fellow PPRuNers, you will find the technical explanation here if digging deep enough.