i have the same problem here. N1 stays at 41-44% during decent. and then fmx says "DRAG REQUIRDE". if it would reduce to 31% or someting like that, no drag would be required. i think it is not common to use the speed brakes during 60-70% of the whole decent path. pressing F1 pulls the throttles back to 31%, but......magic......they come forward again just a few seconds later. the only thing so solve this is turning all autoflight systems off and on again or to switch to level change... it is a bug, i'm really sure...