Hi, as of November 27th, 2017, this is still not resolved (after 2 years!):
Downloaded albums don't show the green arrow, and when opening such an album, the toggle for Download isn't green either.
But when moving the toggle to green status, it immediately shows "Downloaded", because the album was already downloaded before...
Why Spotify isn't listening to these complaints for 2 years now?? I'm on Spotify Premium.