Ah, OK, now I have done some fiddling of my own. It is no wonder that I never see this pattern on my machines. It is related to the default Elyssa theme. Since the default colors are too dark for my eyesight, I have always immediately changed the controls to Human Blue. That changes the panel background, as well as the drop-down volume control. Those "stratifications" do not show up in the Human Blue controls. Now we know from whence it comes, but still not sure how to fix it. Well, besides changing the controls to another them, that is. See if your control change makes a difference on your end. Have fun!