I've had something similar happen with Spotify. Sometimes it (used to?) invalidates downloaded content, probably to refresh the DRM. I was at the airport for a

I've had something similar happen with Spotify. Sometimes it (used to?) invalidates downloaded content, probably to refresh the DRM. I was at the airport for an intercontinental flight and wanted to quickly download another album, so I disabled Spotify's offline mode. At that point it started re-downloading everything over airport Wifi. Needless to say I was not amused.