Any of you with an X58 setup with the G19 probably have the same problem many of us over on the logitech forums are having as well. A simple search of G19 keyboard problems will bring you to the official thread- currently 18 pages long.
The short story is the G19, basically a 200 dollar gaming keyboard with flashy lights and an LCD screen, does not play well with others. Anything from overclocking, SLI, Xfire, plug and play... you name it has been blamed for the keyboard either sticking or missing keystrokes both during normal operations and in gaming. It has been enormously frustrating for gamers and normies alike.
Anyway- no fix is in sight but make sure if you're interested in this combination that you do your research! I plugged in my basic microsoft USB keyboard and it works fine. Consider yourself warned!