Had the same question regarding the throttles, I guess is the way that Boeing/PMDG managed APP IDLE power, on Airbus as soon you select flaps 1, you get and increased thrust on the instruments only, as the throttles are not mechanical driven, I figured out that when selecting flaps 15 and/or Ldg down you get that increment from the throttles, I put the PMDG on a hold a 10,000 ft over the water, and then push FL Change down to 3000 ft with A/T on (or off is the same) and manage the speed toward flaps 15 and between flaps 10 & flaps 15 you would see that throttle increment, same with gear up and down, hope you can see the same.
best rgds.