Sub tasks are easy to lose and hard to keep track of

In the my tasks view the sub tasks don’t have the colour coded project icon. This means it is difficult to quickly see which project they belong to.
It is also possible to lose a sub task by closing its parent task. A warning of unfinished sub tasks would be useful when completing a parent task.

Yes, have a look at To Subtask or not to Subtask to learn more about subtasks.