In the current release of Parallels (8, build 18345) running Windows 7 Professional, the key-chord Ctrl-W is completely non-functional.
I apologize for having posted this prematurely. What has changed, I think, is the behavior of Keyboard Maestro (a macro program for Mac OS) in the current version of Parallels. I had a global macro defined in Keyboard Maestro to move the current window to position (0,0) on the screen and had assigned that macro to Ctrl-W. The problem has been solved by defining a new "Global" macro group whose macros are available in all programs EXCEPT Parallels.
