I'm running Marshmallow 6.0 on a Moto X Play. From a clean installation, I have storage set to 'SD card' in the new Storage menu. I have never downloaded anything, I've only ever streamed. Spotify seems to be successfully using the SD card to store its streaming cache - it's steadily increased to about 3Gb of SD card storage now.
However it's also using 3Gb of internal storage.
Is that normal? It's definitely using the SD card to cache, so why has it *also* used the same amount (3Gb) of internal storage?