I still believe it is problem with PS's programming.
Belief is not proof.
check for updated video card drivers (from Intel's website). if that doesn't work, disable OpenGL drawing in the Photoshop preferences and see how it fairs.
Also, have you tried turning off the pressure-sensitive features of PS?
to do this, open the Brushes panel in Photoshop, then uncheck everything from the left-hand side of the panel.
I agree that it is probably an Adobe problem - the tablet works fine with earlier versions of PS
As before, if I use the pen to draw, and then use the keyboard or the mouse, the pen starts just giving straight lines. However, what I have now discovered is that if I change the size of the brush by using the drop-down brush tab, the pen will start to draw properly again. This works even if the size is changed by only one pixel.
If I use the [] keys the problem remains - it is only the drop-down that fixes it.