I have a D-3 on display in the showroom, with the nav disc locked inside, and, for the life of me, cannot remember how to unlock the display mode. My rep seems unavailable recently, so I must find solutions elsewhere. PM me with the procedure - for obvious reasons.
I had a similar problem with a Demo bought from BestBuy.
To lock or unlock the navigation discs inside the drive, follow the procedures listed below.
AVIC-D3:
While the unit is turned on, press and hold "MENU" and "Back (Track Left)" buttons simultaneously. Next, push and release reset button. Continue to hold "MENU" and "Back (track left)" until the unit reboots.
Then push eject button, NAV disc should eject.
Follow same procedures to lock Nav disc.
Hope this helps.
Thanks! That sounds like the procedure I got it locked in with....I'll try it out tomorrow...if it works, beers are on me, if you ever get down here...
Glad I could help. 
Word.