The map (large screen) of my GPS system locked up two times last week. The voice guidance and arrow indications (small screen) kept working.
I tried to remove the DVD but this did not work. The only thing that resolved the problem was to power off the system.

Today I went to my dealer (to waxoyl my car - www.waxoyl.be if you understand Dutch or French) and they found out (after my Q7 was delivered) that the DVD's are factory placed in locked transport mode.

Might be interesting to know ...

What does this mean exactly?

It means they have to unlock the DVD player when they deliver the car.

Where and how is this done? Is it a software signal?

I don't know. Just got the information from the technician in my Audi garage. I suppose it's a software switch.