Is it normal for the Mercedes air suspension to lower when the car is parked and locked? It rises again once the car is started.

This is a normal phenomenon with the Mercedes air suspension, where it tends to relieve some pressure on the suspension components and settles it to a certain extent. When the car is started the Mercedes air suspension tends to rise in order to compensate for the added weight. Basically the vehicle is re-aligned or leveled. Hence there is no cause for concern unless the vehicle is touching the ground and codes/errors are being displayed on the instrument cluster.