iTunes purchases download twice
Whenever I purchase an album on iTunes the album downloads normally on my MacBook. Then the next time that iTunes checks for available downloads, it downloads that purchase again and I have to delete the duplicates. Also when I preorder an album and download the first few pre-release singles, duplicates of those singles are downloaded when the full album launches.
Why can't iTunes recognise which tracks from a purchase have already been downloaded?
iTunes 12.3.2.35 with Apple Music subscription.
MacBook Pro (13-inch Mid 2012), OS X El Capitan (10.11.3)