Issue with using SD card as download location

[AC Question]

I have a new Motorola Moto G4 running Android 6
I have installed a 32GB Sandisk Ultra SD Card as portable storage.
I have set the download location in Google Play music to be the SD Card.
When I download songs the usage on the SD card increases as expected but the internal storage usage for the app also increases by the same amount.
This also happens on another app I have within which I download data.
Any ideas why this is happening as it kind of makes me having an SD card pointless?

 

[dpham00]

What's shown in the app manager is both data on the internal memory and sd card