Unwanted Diagonal lines Appear Spontaneously Windows10 Huion H610PRO

I wonder if anyone can explain the unwanted diagonal lines which appear almost every time I touch the pen to my Huion H610PRO.

It doesn’t happen if I use the mouse to draw.
It doesn’t happen if I use MyPaint version 1.0.0

But MyPaint 1.2.0 is unusable (for me).

I’ve tried uninstalling and reinstalling.
Tried with Windows 7 on one laptop.
Tried with Windows 10 on a newer one.
Tried with the USB-connected pen, and a wireless pen.

Those lines keep appearing.

When I first started working with MyPaint, the lines didn’t appear. It’s a recent phenomenon. The pens work fine with all other art programs I’ve tried (Gimp, Paint, Photoshop, DrawPad, etc.) Can anyone suggest why this happens?


Hope you don’t mind me replying to my own post. I’ve just seen a thread elsewhere which looks very similar to my post above. Does the extra information help?


By the way, I’ve tried MyPaint w32 but it won’t open in Windows 10, and the debug won’t load, either. Fun, huh? Sorry!