Mstn CE Update 11--Visual disturbance

Hi,

I was doing an "extend line" command in a 2D file when this suddenly appeared.  What would cause it, and how do I debug it?

It corrected itself when I did a refresh view.  The black dots appeared as I moved my mouse.  I'm using an AMD FirePro W5000 video card with the 2018.Q4 drivers.

--Thanks,
--Robert Arnold