Paint Shop Pro :: Lifting Bamboo Pen Stops Painting?

I have a Wacom Bamboo Pen and Touch on Windows 7 64-bit and it appears to work fine in Windows on the desktop and in MS Paint. I can drag a box on the desktop, scribble in paint to my heart's delight, etc.

In PSP X4 the pen works...briefly. If I keep the pen down enough to make the red light appear on the tablet (to say it has detected the pen is close) it will happily draw in freehand with the paint/airbrush. If I lift the pen high enough to go out of detection range and put it back on the pad, PSP won't paint. The mouse will paint and the pen will work with tools like Pen or Flood Fill and in other apps but freehand doesn't work.

To get freehand back, I need to click on a button, tick box or other window control on the screen with the mouse. Then I can draw freehand again until the pen goes too high.

The PSP when it goes wrong like this is strange. Hovering the pen within detection range moves the cursor as normal, but on pressing down the 'dot' (or circle depending on brush size) stays where it is without making a stroke. The cursor moves around normally otherwise without applying anything to the image.

I've tried to re-install the drivers with a new copy from the manufacturer's site and removed Windows Tablet Support but nothing works to resolve this.