I loaded a new flight by 1st loading the P3D default flight...than changing airports and aircraft to the 8. Since reading your reply, above, I played with it a little longer as follows (hope this helps):
Aircraft would load with engines running
Found if I left the engines running doors worked correctly
When I went to cold & dark, doors worked incorrectly as reported
If I activated external power doors would function correctly
I know the checklist has to activate external power, as one of the first things, but I was not actually preparing for a flight last night and today...I was really just wanting to watch the new GSX load passengers since I have been flying GA aircraft for the last few months and had not seen the loading of passengers animation. So, I guess it is somehow tied to having power on the 8 operating. Any way...now that I know that I can go ahead and plan my flight.