My Dell Studio XPS 13 has a brightness up & down buttons (Fn + up arrow / down arrow), as do most laptops have. It's running Windows 7 64bit and I've installed Windows Live Messenger (build 14 and something) on it.
When I hit Fn + down arrow, to reduce screen brightness, the Messenger window pops up. That's true whether it has been running in background (system tray / minimized) before or not.
Note, to make messenger hide itself to the system tray, I've set it to Vista Compatibility mode. I don't think that has anything to do with it though, since if I shut compatibility mode off, the problem persists.
There's a thread on the matter here, but with no solution.
Stop Intellitype when using internal keyboard. See detailed howto here.
EDIT: Some new findings on the matter -
If I exit messenger entirely and restart (or simply stop) the service "Windows Live ID Sign-in Assistant" the problem is solved until I run messenger again. It persists even after entirely closing messenger, until I restart the said service.
The above service "Windows Live ID Sign-in Assistant" actual name is wlidsvc.
There's no shortcut defined for messenger, nor is there any other hot key in its preferences.
- I'm not sure if it's relates, but some of the Fn keys are not working - Fn + F1 doesn't put the machine to sleep, Fn + F3 doesn't show battery status.
- Problem probably relates to conflict with IntelliType Pro. See my answer below.
- Said conflict also causes Undo command when disabling Wireless (Wireless touch button), and other side effects for various keys.