Synced content doesn't play offline

I have synced 60 GB of various content to my windows tablet. When the device is not connected to the network, and I launch the app, the synced content shows as available, but when I start playing an item, the player opens, but nothing plays.

However, when I connect to a network, then relaunch the app, choose an item to play, that item plays right away, playing the synced version.

What gives?