Parrot Minidrone - altitude sonar

Also with the newest 'Simulink Support Package for Parrot Minidrones' (version 21.1.3) I get very strange measurements from the altitude sonar sensor. Within the following plot I lifted the drone slowly from earth to ~1[m], stop, to ~2[m], stop and back to ground. For the plot I used the deliverd 'parrot_external_mode' example with a scope connected to 'altitude_sonar'. My drone is a 'Parrot Mambo Fly'. Can anyone confirm if this sensor output 'normal' ?