Microsoft is not quite done with Xbox Music for Windows Phone 8.1. Tonight, version 2.6.657.0 is live in the Store, and it looks to be a rapid-release fix for an issue affecting some users.
No other details were posted on the Xbox User Voice page, so it is safe to surmise no new features were added. In addition, seeing as this is a minor number change from 2.6.656.0 just a few days ago, this looks to be more about addressing a very specific bug for some people.
Full story from the WindowsCentral blog...
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