If I get/want a speed change, I set the new speed in the window, press V/S, set 0 fpm (press to level off), and 10 kts before reaching the speed, press LVL CHG (pull for open descent). Much more predictable deceleration, so much more predictable path.
I never did that but, if I did, I'd set vs -500 not zero in controlled airspace as levelling off would not be complying with your descent clearance.