According to the official Xbox Music blog,
A new release is available today for the Xbox Music app on Windows Phone 8.1. You may have noticed it has been more than two weeks since the last update was released. Updates will be less frequent now that the team is also working on new features that will be introduced in Windows 10. Rest assured we will continue to update the Xbox Music app on Windows Phone 8.1 based on your feedback. Expect an update each month. Please continue making your feedback known on User Voice, in store reviews, and elsewhere on the Internet. We’re listening!
The changelog for the new update, v2.6.414.0, is:
Thirteen of our top unexpected app exits (e.g. playback during sync, changing filter with selected songs)
Album and artist art issues:
Some local tracks not showing album art in Now Playing
Album art flashing while shuffling large collections
Background artist art flashing
Inconsistent display of album art when offline
Local or sideloaded albums not showing album art in Recent Plays
Content sync interruptions causing all future syncs to fail
Deleted songs don't always get removed from your collection
Unable to playback albums in certain circumstances
Inconsistent sorting of songs that start with an article (e.g. “A”)
The team also notes that they 'brought back the buy option for individual songs which disappeared last week'.
Watch for a short index rebuild when you start up the new version; the main interface remembers what you listened to most recently; you can now buy individual tracks again...
Many users still complain online that (Xbox) Music isn't as flexible as the old Windows Phone 8 (Zune-based) client - they probably have a point, though performance and functionality is easily enough for the vast majority of normal users, I contend. Not once have I found that the client didn't do what I wanted (i.e. play my music). What about you?