Consider the following scenario:
In SharePoint 2010, you create an approval workflow that is configured to start automatically when an item is changed and is also configured to update the approval status of the item after the workflow has been completed. In this scenario, after the workflow is completed, the approval status of the item against which the workflow was started does not get updated.
This behavior is by design. The "Update the approval status" option in the workflow is a "Post-completion" step, which means that the step is performed after the workflow has already been completed. If the post-completion status updates the list item, it would trigger the workflow again since the workflow is configured to automatically start on edit, resulting in infinite recursion.
If you intend to use the approval workflow for content approval, please uncheck the "Start this workflow when an item is changed" option in the approval workflow definition. This will ensure that after the completion of the workflow, the approval status gets correctly updated.