Please feel free to use my experience in your discussions with GM. Let me know if I can be of further assistance.
I took delivery of my 2013 in December of 2012. My trunk started opening not too long after that, typically in my garage, but I did find it open in a parking lot at least once. I've replied to one or two threads here to document my experience, and it was in one of those threads that I learned of the two-shot relay. I had that installed at my dealer when I had the 7500 mile service done (I'm pretty sure of this, but I can check for sure if it's important). Since then, the trunk opening has happened twice, both times in my garage. I have my car set to lock automatically shortly after I exit the car, so unless the car somehow mysteriously unlocked itself, it was locked when the trunk opened.
Incidentally, I have not had the new trunk key pad installed. Moreover, my trunk key pad does not work very well. If I press it twice at the same speed I press my key fob, the trunk won't open until I press it at least a third, and sometimes a fourth, time. I'm not sure if that is related to the current problem, but I thought I'd mention it. It's such a minor annoyance that I haven't requested that it be fixed.
Good luck, and I'll be watching for further developments.