I noticed than when I move the throttle forward out of “beta” range to idle, power seems to surge, increasing aircraft taxi speed at a time when I’m trying to slow down. The power level does eventually drop to idle. I’m using Saitek Throttle Quadrants and have programmed the button (Throttle fully retarded past idle) with the Throttle Decrease (repeat) command using FSUIPC. Has anyone else noticed this?

As IRL you have to move the powerlever carefully and real slow between beta and idle to avoid 'surging'. 

Set idle power and hit F2 a single time, the prop will enter the beta range but power will still be almost at idle.

Selecting idle from this beta range shouldn't result in any surging.