I've had the same problems on my tablet PC, also with GIMP 2.4.2.
I remember it working fine on Vista, although I'm not sure whether I
had the same version of GIMP, it may have been 2.4.1
I did test it in Adobe Flash as well to see if it was an issue with
the pen, and had the same trouble, so I think the tablet driver is to
blame. I id try reinstalling it but this ended up making the pen not
work at all, at the moment I have uninstalled Wacom's driver again and
am using the Windows XP built in driver, which lacks functionality for
pressure sensitivity and the eraser.
I will try installing the driver again and will tell you how that works out.
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