Yeah, that’s what was odd: from the pet palette, I tried Move node; Offset edge; and both Add/Subtract polygon shapes, but the cut corners were persistent. With Offset edge, they would just move to wherever the new edge was. With Move node, I couldn’t drag one over the other to make a 90deg corner. It just refused/reverted to the cut corner.
When I pulled the node for the ridge end to create a diagonal gable edge, the corners would disappear. But then they’d return when I pushed the ridge end back to an orthogonal location (for a rectangular plan shape.)
mac ACv26/4034, US solo, Ventura 13.1, 2020 iMac