Download to SD - eating internal space??

Using Apple Music with a cheap Android device - only 600 MB free so I was keen to use the new download to SD feature and stuck a 32gb card in.

Everything seem Ok until I noticed that every time I download a track to the SD card I also lose space on the internal memory - and not a small amount

.

I did some empirical testing and downloaded approx. 50 tracks - lost a couple of hundred MB on the phone and used slightly more on the SD card. I would guess it is downloading to a temporary file on the internal memory before transfer to the SD but is not cleaning up properly.

Unfortunately, this makes the feature almost unusable - I tried to download a modest playlist to the SD card and the phone rapidly ran out of memory.

Anyone else tested this?