Thanks, Peter, for pointing out this. I picked something else rather than the items on the title bar. 

Now I see this is the known Vision2 issue that the PND line is redrawn by xor mode. When the mouse moves, a new line is drawn to wipe out the old line, if in between the context is redrawn, what you see happens.

The solution on Windows is that Vision2 draws the PND line in a light window. On Linux, a solution needs to work out.

Now suspend it until Vision2 fixes the problem.