ask for "level change ...knots"
It does not change the thrust setting, has nothing to do with Vnav, so why ask for level change .....knots, why not just ask for the speed?
Isn't it commanding "Bug Speed plus 20" which is usually V2 + 20? If you place the autopilot on, the bug jumps to the present speed, and the mode changes to LVL CHG anyway.
If you don't select a mode change, either by placing the autopilot in command or selecting LVL CHG, but just increase the bug - will it not command Bug+20 as it is supposed to? I haven't tried it.