Waypoint Mission behavior, steady slope instead of rapid altitude change?

Hi,

Test Setup: Mission with two waypoints. WP1 (100m), WP2 (20m) between them 350m.

What I want: Fly in a straight line from from WP1 to WP2.

What the plane does: Immediately after WP1 a rapid alt change followed by a gentle slope.

Between “dive” two and tree I changed GLIDE_SLOPE_MIN from 0m to 1000m, without a change in this behavior.

Does anybody have any idea?