1) Create a task and add someone to follow this task. The task is automatically shared with the person.
2) Create a sub-task for this task. The group of people sharing the main task is copied to the sub-task. However, this is not the case for the group following the task.
We add people for sharing the task because we think they should be informed of changes. We create sub-tasks because they are related to each other or to the main task. Therefore it is likely the people following the main task, also like to follow the sub-tasks.
The drawback of excessive following is of course the number of messages received. However, the person can always choose to un-follow. The 'damage' done by forgetting to add the same followers for the sub-tasks is in our opinion larger than having to many messages.
Moreover, we think that the current functionality is counter intuitive and unexpected.
Therefore we suggest to include the followers of the main task to any sub-task created.