It includes a fix for a crappy situation in which iTunes Match (read: DRM-free) songs were swapped for Apple Music (read: DRM’d) songs. Jeremy Horwitz over at 9to5Mac explains the delicate procedure for remedying this, if you were affected:
If you want to restore a downloaded, Apple Music DRM’ed track to normal, DON’T just delete the DRM’ed version of the song from your iTunes library. Try to do this, and the dialog box above will pop up. Hitting return or the blue-highlighted button will obliterate the track from both your library and Apple’s servers, such that you might not be able to get the track back.
Instead, Apple says, you should control-click and choose “Remove Download” for all tracks that were incorrectly downloaded as Apple Music. Then control-click again and choose “Make Available Offline” to re-download them correctly, without DRM.
Let me get this straight: the bug could taint portions of a local library with DRM, and the removal procedure requires exact steps that are counter to what you may be expecting, and that following the steps you may expect instead will nuke the track almost entirely unless you use another workaround explained by Horwitz in his post? This isn’t acceptable at all.