Upvoted; I have not tested this across multiple autopilot systems but can confirm it occurs in the Cessna 172 G1000 as well, as seen below:
In Flight Level Change (FLC) mode, pressing the nose down button should increase the target airspeed while pressing the nose up button should decrease the target airspeed. This is because FLC mode adjusts the aircraft’s pitch ot maintain the selected airspeed. Pressing the nose down button commands the autopilot to increase airspeed by pitching the aircraft down. Pressing the nose up button commands the autopilot to increase airspeed by pitching the aircraft up.
The Nose Up/ Nose Down behavior in FLC mode is currently bugged because it reverses the behavior of the buttons as OP explains.