30 second fix: what that nub is a cutoff nib on the lathe when it cuts the part off. Take a approximately 400 grit piece of sandpaper, lay it flat and pull the button along it with the face down, You'll get a nice cross hatch finish on the button to boot. I can do up a quick demo video if you'd like on monday, its painfully easy.
I'll put the dremel away and I'll give it a whirl