Sorry for the long delay, I just didn't find the time. I did some testing and it seems that no keystroke whatsoever goes from Win7-Explorer to TapTap. I guess, answer 1 would be true.
The issue seems to occur in:
MS Paint 6.1 (Build 7600)
But all the other apps work fine (IE, Notepad, MS-Office, Firefox etc). I wouldn't care for paint, but in Explorer it really sucks.