when you click on a subtask with your mouse and then "Tab + → " you get to the sub-subtask. After that you can go back with “Tab + ←” and you are again in the subtasks - that´s great !!!
Unfortunately you are lost after that. it is not possible to make any movement between the subtasks with the keyboard. i am stuck in the subtask.
am i doing something wrong? I always have to click on the subtask to mark it again.