Created attachment 144948 [details]
comparison screenshot

It looks like a DPBB/scissor interation issue.

The screenshot on the left is a replay of a faulty trace with dpbb disabled.
On the right the same trace, at the same point but using dpbb.

The last executed commands are:
   glScissor(3, 3, 480, 144);
   glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, 1);

As you can see, the purple area on the right doesn't honor the defined scissor
area.