Since version 1.4, the Professional add-on has had a new feature to allow you to use the same image already obtained previously, but without downloading it again, if it has the same name.

This can be confusing because different images, whether from different sites or not, may have the same name, and then different posts will use the same featured image.

Just use the WordPress standards to avoid this behavior.  You’ll upload all the images, but won’t end up repeating them incorrectly.