Sorry can't help you on it not ejecting, but was going to ask if that dvd had a label on it maybe, making it thicker?
As for playing DVD's, I have not done this, but if you search around, there is a series of buttons on the right that you press and it allows this.
I don't know if that works on the nav, but sure would be nice if it did, as our nanny nav systems suck in that regard! (not that I use it much, but when I'm on a long trip and driving on the interstate and the thing is set wierd to keep trying to make me exit on every one, it would be nice to change it while driving...What happens if you have a passenger and they want to help navigate? IMO, at the minimum GM should've tied into the pass. airbag sensor on th seat to let you do this when a passenger was onboard, if nothing else. I'm glad I don't need or use nav systems much other than for fun, otherwise I'd be super disappointed in this pos we have to deal with, lol.