The 8.4" screen on my 2012 R/T doesn't go blank when you shift out of park, it goes blank when the vehicle is in motion. When I am stopped at a stop light (or stop sign) but am still in drive, the video goes back on. It stays on after I start moving until about 2 mph, when it blanks out with the sentence "video not available when vehicle is in motion" or something along those lines.
Related question: in the rear seat entertainment menu. there is a button on the top left for "disc 1" and a button on the top right for "disc 2." Am i right to assume that the "disc 2" button is for Journey's equipped with a rear seat DVD player (not just a rear seat screen)? As far as I can tell, i do not have an additional DVD player in the rear, just a screen and the HVAC controls (although on the back of the center console, I have A/V input jacks for a game system, etc.).