A task board inside one project shows that project’s own columns. Open a project, switch to the board, and it could draw a single column named after the project with every task piled into it — telling you nothing about which of them was Home and which was Work. Grouping by page is the ordinary way to arrive there, and a project is a page, so that grouping could only ever produce one lane. The board now falls back to grouping by area whenever the grouping would divide the view by the very thing it is already narrowed to. And inside a single project the lanes are the ones that project actually uses — two tasks in Home and Work draw two columns, not two columns and four empty ones. On the whole board every area is still drawn whether it holds anything or not, because there an empty lane is where you drop a task to give it that area; inside one project that argument does not hold, and an area is still one click away on any task’s own chip.