thank you @jpvianor for the workaround. The Wacom tablet seems to send an avalanche of key commands when hovering with the pen over the surface, when the paintbrush or gradient tool is selected. Tapping the pen on the left side on an empty space stops this, but it's a workaround.
When doing another gradient, the flickering starts again. And I can only edit one point, upon lifting the pen from the surface the flickering starts again and the other gradient points cannot be edited at this time.
This behaviour only happens with Gimp. Rebelle, ArtRage, Mischief, Davinci Resolve, and all other programs work perfectly fine with the Wacom Intuos 4 L. It's an old tablet and an old pen, but they are reliable and still usable. I'll post the solution here when I found it out.
Edit:
well it seems there is no easy solution. Ink is deactivated in the Wacom driver for all programs, not only for Gimp. The flickering is reproducible with a gradient tool, editing one color. Then the flickering starts, and can be stopped with a right-click with the pen also. Possibly it is an interference with the mouse driver (M.M.O.7, old driver, no more supported) or another driver like the 3dx Ware. I don't know.
When doing another gradient, the flickering starts again. And I can only edit one point, upon lifting the pen from the surface the flickering starts again and the other gradient points cannot be edited at this time.
This behaviour only happens with Gimp. Rebelle, ArtRage, Mischief, Davinci Resolve, and all other programs work perfectly fine with the Wacom Intuos 4 L. It's an old tablet and an old pen, but they are reliable and still usable. I'll post the solution here when I found it out.
Edit:
well it seems there is no easy solution. Ink is deactivated in the Wacom driver for all programs, not only for Gimp. The flickering is reproducible with a gradient tool, editing one color. Then the flickering starts, and can be stopped with a right-click with the pen also. Possibly it is an interference with the mouse driver (M.M.O.7, old driver, no more supported) or another driver like the 3dx Ware. I don't know.