I really hate to have to say this, but it has started up again. I have tried turning off the firewall, turning off Windows Defender, it makes no difference. I have even tried using lower screen resolutions and color schemes.
The interesting thing here is that the problem only occurs with one particular menu (the right-click menu for the blue tray ball) and on that menu there is only that one point that leaves "leftovers". If it were the graphic card you would think there would be other problems as well. There may very well be an interaction with the graphic card, but to say that the graphic card is causing this would be going too far.
I have been using this PC for two years and this is the first such experience of this nature that I have had.
Here is the picture again so you don't have to scroll to the top of the page.
I really like avast! I would really like to find out what is causing the problem.
Dave