Arduplane Terrain Follow no lookahead

Hi there, I have set up the terrain follow on my arduplane and have set the TERRAIN_LOOKAHEAD to 2000m now if i plan a flight and set the TERRAIN as height reference on a waypoint mission and look on the height graph from ardupilot, it shows the exact terrain line with the offset of my preset height. In a video from painless360 (MIssion Planner Secrets and Hidden Features - YouTube) at this timestamp you can see that it “flattens” out the terrain. What am i doing wrong? Any suggestions?

@Michael_Oborne Might this be a bug in the software? I really can’t find a solution for this… Also updated to the newest release of the plane fw.