Fc38 kde plasma x11 nvidia - Win key + shift = red lines follow mouse

I’m using blender-2.79 and have assigned Win key for loop select and shift key modifier for multiple selections however now pressing that key combination draws a red line on the desktop wherever the mouse cursor moves. I have to force the desktop to redaw in order to make it go away.
Is this some kind of new kde presentation feature or something?
I couldn’t find anything in advanced keyboard settings. Any ideas as to the cause and how to make it go away?

I solved this. It turned out to be a desktop effect “Mouse Mark” .

I’m just glad it’s not some nvidia wierdness.