That's an interesting read and this comment
The test pilot observed that ‘the rate of flight path change could be alarming especially within a [degraded visual environment] DVE.’
highlights that the crews were lucky that the problem was identified on a training sortie in good weather rather than during a rescue at night or in poor weather.
It does seem rather overkill to want the FMS to do a job the AFCS can already do - when you press TD the speed automatically reduces to 80 kts (if I read it correctly and it is similar to the 139) in the descent and it is unlikely you will want a speed more than 60 kts for a sector search at low level so why have NGSPD at all when you have GSPD available to be set once at the correct height for the search?
This overdoing of automation for the sake of it seems counter productive and results in AFCSs that are so complex and have so many modes and parameters that easy, intuitive operation of them becomes more difficult.