Correct, everything completely updated. To provide more specific information on the issue, playback doesn't stop immediately after the screen goes black, but won't advance to the next song after the screen goes black. For example, if SongA is being played when the screen goes black, the music ap will not start playing SongB while the screen is black, even if SongB is the next song in the queue. As soon as I wake the Surface, SongB starts playing automatically, even if playback has been stopped between songs for 20 minutes. Ideally the expected behavior is that playback will continue uninterrupted between songs even when the Surface is put in standby, similar to how playback occurs on cell phone music aps.
I've noticed that this playback interruption is not consistent, but almost always happens when the music ap has trouble connecting to the internet (despite playback on locally stored music, rather than streamed or cloud stored). In general the music ap has all sorts of problems, such as the inability to search local libraries.