there was a "patch" to 5.12 that fixed something on the original 5.12. so if you had the original 5.12, i believe that second patch (i don't have the version # in front of me) was to fix some serious bugs that were causing the screen to black out, randomly reboot, or not turn on at all. in my case, the original 5.12 somehow wouldn't start my 17" screen but everything else was "on". that update was released within two weeks of the original i believe.
we were backing out of garage, in a hurry to get to airport and screen never came on. i tried to reboot, nothing. so we pulled it back into the garage and got out and took the benz because we couldn't control most functions. when i got back after dropping off my husband, the car was STILL running and had been running for 90 minutes. i thought it would shut down once i left the seat and no key was present, but i guess not. there was a massive condensation puddle from the AC running that long. i got back in and tried to reboot, do a bunch of things, nothing worked. long story short, i called san diego SC and they sent a ranger out to shut it down and install the patch to 5.12 which had just been released hours before my mishap. so far so good with the newer 5.12.