Hi!, this is what i do, in order:

1) Load the default cessna and turn it off (Engine, battery, master, avionics, mixture)
2)Verify that the cessna is dead (Cannot turn lights, gps screen is black, etc)
3)Load the CS757
4)The plane loads in 2d view. then, one by one i open and close all the 2d panels (Animations, overhead, radio, pedestal, etc etc... all of then)
5)Use the 'A' key to cycle all the positions
6)Use the 'S' key to cycle all the views
7)Then, i verify: All is dead, but the CDU screen is turned on. If i turn on the position or navigation light, the light will turn on too.