The region height editing basically works correctly, except for these three rectangles at the southwest side of the world map, each of which acts as though the region editor wasn’t even there. (In the view, the top of the screen is toward the east; north is to the left)
The cursor is pointing to the middle of the three non-affected region. There’s a smaller region to the north, and a larger region to the south. No clue as of yet just why these rectangular regions aren’t being affected by the region editor..