I tried all of the things you suggested. SendInput, SendEvent, and sending {LWin up} didn't produce any change in behavior. SendPlay resulted in no keystrokes to the program. KeyWait, LWi ...
I'm running Windows Vista Business x64 (release version 2006-11-16) and AutoHotKey 1.0.46.05. I use the Windows key as a shift to activate many actions. All worked well with Windows XP. With Vista, ...