Been trying to tell you. It has not changed, I'm not levelling on a flat Islæand (Why the hell would I be levelling a flat land, it's already leveled.)
I'm simply saying that I've been doing nothing but terraforming in-game up to the construction patch that was almost 4-5 weeks of terraforming 12-16hrs a day (sometimes catching fishes for foodses)..

I got no idea what happens at you, it might be you that are bugged, it might be the ground at you that are bugged. But it is definately not something new. Weird non square corners have been here for as long as I have (at the very least).