WAYPOINTS 2 ALTITUDE ANOMALY?

[Micktss]

There seems to be an issue with altitudes of waypoints. The height of a waypoint on my system is limited to 400ft above the take off point. We live near a disused quarry which is 900ft above take-off. If set as a waypoint the drone would not clear the quarry. The legal altitude in the UK is 400FT above GROUND LEVEL. I have found a work around by changing setting limiting the Maximum Altitude of the drone to 121m above ground to 500m this results in a warning that the legal limit has been exceeded but allows the change. The waypoints can then be adjusted so the drone will clear the Hill!! Am I missing something or is this an anomaly?