Here's a weird one. Just recently, if I hit Command + Q to close an application and then let go of the keys, it's like I never let go of the keys and the system tries to quit everything that's open. Then it just winds up on Finder with the Mac 'bottle' sound firing endlessly. I'm forced to hard boot my computer afterwards. To my recollection, I haven't installed/upgraded anything recently that may have caused this. Though I have gone through several updates via the App Store, which haven't required a reboot, and as I've been working on a design project for many days - I haven't closed any applications in a while. So it's possible that one of those prior updates did something and I'm only now realizing it. I'm on a 2008 Mac Pro running 10.8.4 and all patches. Any idea what's going on?