A user with the role as a project manager is able to reopen an ended task. By doing this, the individual task status of the user is affecting the ability of editing the task again.
Confirming a task
If a task is initially set to "unconfirmed" after import, no one can edit the task. It must be confirmed by either an assigned user or a pm in order to be editable. The assigned user must be able to edit the task, from the workflow point of view.
Viewing a task
Each user is able to open a task for viewing regardless of his role and his status in the workflow, which is allocated to him. The user with the role as a project manager is always able to open all tasks for viewing.