Summary:
When a project or task is closed, all the associated tasks and sub-tasks are closed automatically. Now, if this project or task is re-opened, all the associated tasks and sub-tasks that were closed along with the project/task will be re-opened.

Resolution:
It possible to re-open a closed project or task while leaving the task or sub-task in closed status. To achieve this, close the Task/Sub-task before closing the Project. This will ensure that the Task/Sub-task remains in closed state even when the Project is reopened.