terraforming with Alt held down and dragging NE jumps in large increments.
If you drag SE you can go in 1 block increments, but dragging NE (with the green preview box while Alt is held down) makes large jumps often and forces a uniform scale of the area instead of actually growing only in the direction you are dragging. In other words it jumps in large increments and if you move the mouse horizontally, it also grows the box vertically.
Reproducible on Fields of Isis when terraforming the SW vertical wall. Terraforming near the tip of the mountain range. Likely happens in general, but that's one place it can be reproduced. It quite possibly might have to do with having terraformed a high flat area, then dragging the mouse (with Alt held down) NE. When the mouse goes from the high ground to the low ground during dragging, this seems to happen.
