You need to provide exact system info. This is not normal, but who knows, some input device driver for a tablet or a configurable mouse could send some wrong signals or a misconfigured graphics setup cause a wrong click area to be registered...
I am running Windows Xp (32bit) with Wacom Intuos 3, Logitech Mx500 Mouse, has a 256MB Quadro FX 370 (nVidia) and Intel Core 2 Duo E8400. It's a very had thing to reproduce it just happens out of the blue, mine isn't the own system this has happend on. Other collagues have had this issue too.