Normally a task tooltip appears below the cursor. When a lengthy tooltip appears near the bottom of the grid, it moves up, to the right of the cursor, so that the tooltip is not truncated.
However, it moves to a position where its leftmost edge is directly under the cursor. This makes it impossible to select a task, because the click is on the tooltip, not the task. A related problem occurs near the bottom right of the grid, where the tooltip appears directly under the cursor and again blocks viewing and selection.
It seems like some usability improvements could be made here. The direction in which a tooltip is displaced to avoid truncation should depend on the position of the task relative to the edges of the grid, so that the tooltip is fully visible and does not block viewing or selecting the task.
Just a suggestion. Great product!