So the default logic is that the overrides folder acts purely as an override. Meaning if it exists there it replaces the media being presented to you.
However, I can see it being interesting to allow users to:
not download files if they exist in overrides
give downloaded media priority and fill in the blanks with overrides
As for it downloading even when not selected, I will both add logging for this and double check this week during testing. Thanks @Creezz67