found in nightly r7340 paksets: pak128, pak128Britain, pak64
Since the new landscape allows ground climates the user may like to change low water areas to ground. If he uses the "show grid" option he didn't get a grid on the water.
On the other hand you get a grid on "sliced map view" at underground areas (only pak64 and pak128Britain) every time, the "show grid" button did not have any use. At pak128 there is no visible grid at the underground as long as there is no way build. Reason maybe the black kind of grid.
That is not exactly consistent in the logic of the button "show grid".
Indeed, not seeing the grid in underground mode is a problem.