Since installing the TrackIR drivers (version 2.11 beta 4), use of the modifier keys Shift, Control and possibly Alt (haven't found a good way to test the alt key). As best as I can tell, if I have any (or several) of these keys held down for a time period of a second (approximately), the computer freezes up when I press a mouse button. It only unfreezes when I release shift/ctrl/whatever.
This only happens with the drivers loaded. None of these buttons are set as hotkeys. The time period was set to a second (the same as how long the modifiers work) but setting this to any other amount of time still doesn't change the one second it takes to die.
This happens even if the drivers are disabled (via F9) and regardless of mouse/enhanced mode.