This is the kind of simple but frustrating bug that REALLY tees me off!

A few days ago the following started to happen in Windows 7 all of a sudden:
Clicking on a taskbar shortcut brought up the properties dialog for the shortcut.
Double clicking on a folder in an Exploder window brought up the folder properties dialog.
I got Windows back to normal only by doing a system restore from a restore point.

GRAW!

So the same freaking thing happened to me tonight. It really throws you when it happens because to open anything you now have to right click and click on Open in the context menu.
I realized something simple, though. You can force the left mouse button to bring up properties by holding down ALT. It's a simple keyboard shortcut.
So I pressed and released the ALT. All of a sudden the left mouse click was back to normal!

The ALT key was acting like a freaking stuck shift key.
Possibly it is my VOIP application I am debugging. It monitors the SHIFT and other keys to detect hot key presses. But this had never ever happened before this week.
I also observed one odd thing, maybe not related, with respect to the ALT key. If an Explorer window has focus, pressing the ALT key toggles the display of a "text" menu bar (the CUA style menu with the File, Edit, View, etc selections.)
Any thoughts or theories about the weird stuck ALT key issue? I can't induce it manually through pressing the ALT key. The ALT in normal use acts like an "SPST" switch, not a shift key.