Workflows attached to service tasks

At the moment, if a deadline on a task, for instance on an accounts preparation task, gets extended, the system creates another task with the new deadline and marks the current task with a banner 'To Delete'. Users are supposed to delete the old task. However, if a workflow is attached to the first task, all the subtasks progress is not moved across the new task and therefore is lost. The new task has a workflow with all subtasks reset to 'To Do'. It would be useful if the system asked or moved automatically all the progress on the existing workflow subtasks to the new task.