How to stop XBox Music commercials while playing music in collection?

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http://superuser.com – So i decided to give Xbox Music a try, and played a song in my collection. Then moved to another song and a commercial started playing. Huh? Searching revealed others with this problem, but i didn't see any answers. Yes, i know Xbox Music plays commercials when streaming free music that you don't own, but this is mp3 music i own, on my hard drive, in my collection. MS claims "You’ll never get ads when you’re playing MP3s that are on your PC or when you’re playing music you bought from Xbox Music." (FWIW, this is running on Windows 8.1 Pro, though the problem seems to have been reported (HowTos)