I noticed this yesterday - whenever I copy a page that had tasks on it, the old tasks are continuing to show in my task reports.
This is happening even if I remove all of the tasks, add new ones in a separate area, or change the dates on those tasks.
They are all showing up in the task reports with the new page, but the old task content. Clicking through to the page is only showing the new tasks and not the old ones.
Is there a cache that I might need to clear or something?