When I look at a map made in the nether and am in the nether, the marker on the map spins in circles, similarly to the way compasses and watches do, only choppier. This makes it hard to find much of a use for nether maps at all. I discovered this bug on a vanilla server I set up personally on my own computer, connecting via "localhost", not my public IP. The attached video shows the spinning marker. Earlier, the green waypoint markers were spinning as well, but after logging in and out of the server a few times they stopped spinning. I didn't get a video of the green markers spinning.