Faulty rendering in Volumetric Rendering example

In the Volumetric Rendering example, if you rotate the map so that the water edge is at the top-right of the map, you can see a faulty rendering in the wall of the border behind the water. This is best observed with using the high quality option for the map.

Expected behavior:

Nothing should be able to render on the border wall.

Observed behavior:

Something renders on the border wall.