I stand corrected - looked at it at work last night and on the monitors it looked like a door - my first thought was it was being used for skydivers.
Having now had a chance to look it at it at home you can see in the frame by frame its a black rectangle painted on the fueslage.
didnt mean to get everyone worked up - it is an object lessons in PIO's though. Can believe that if it was a student and instructor that the instructor didnt take it away from him long before it got to landing.