RNAV contant climb v. alt constraint
It, the FMS, does not matter nor does it care whether or not you shallow climb to waypoint or climb and then level off due to a constraint.
If you shallow climb to a constraint as part of an RNAV procedure and you have experienced climbing to waypoints in a hard climb then levelling off at the waypoint, to continue climb after the waypoint, that is probably because your waypoints were close together like in a SID.