Suddenly can't place any more blocks along a wall
At a certain point on making a long wall, suddenly there will be a point where I can no longer place blocks on the wall to make it longer, or taller or thicker. I can place new separate blocks on the ground next to the wall, just not touching it. This has happened once in a previous save, and again in a current one.
The attached folder has a save game with the problem. The area of the castle with the bug is at the end of the long unfinished wall. Where the wall stops being two blocks thick, and becomes one block thick, is where no more blocks can be added anywhere past that point.