Sub tasks cannot be deleted
Create and save a task, then open it, go to edit mode, and add a subtask in edit mode. Save the task again to close it.
Expand the task's subtasks and tap the subtask to edit it, then tap delete in the lower right corner.
Observe that in the tasks list, the task's subtasks counter still shows 1, but tapping it expands an empty subtasks list.
Now open the task and go to edit mode, then go to the subtasks tab.
Observe that the subtask is still shown.
Trying to delete from the edit view's subtasks list shows similar behaviour.
Tested in version 102030006.