<b>Version: <Kenneth, what is the frequency?></b>
<b>OS: <please tell me it's not XP></b>

What steps will reproduce the problem?
(1) go to https://jsbin.com/jagigoniso/edit?html,output
(2) turn on "Enable Paint Flashing" in devtools
(3) watch table get painted over and over forever

What is the expected output? What do you see instead?

Table should only be painted once.

I've done some investigating. For the bug to occur, you need:
<colgroup span=2> with a background-image with size 100%
<td colspan=2>

My guess is that interaction between image loading code, and size computation of colgroup causes some repaint flag to be set.