The behavior described in the linked article sounds like an out and out BUG, and a very major one at that. Rental tracks should NEVER overwrite purchased/ripped tracks on your Mac or PC. Adding "duplicate" rental copies of albums to your library is one thing. Destroying / corrupting purchased music is bad, and if iTunes has this bug, one wonders why Apple didn't catch it during testing.
http://www.imore.com/no-apple-not-adding-drm-songs-your-mac-you-already-own
Also, this is how disinformation like "iCloud Music Library is DRMing all the music on my Mac!" gets disseminated. Because if you upload all your music to iCloud Music Library, then delete it, then redownload it to your Mac, iCloud is going to assume you're downloading that track onto an auxiliary device, and send you the matched tracks. Which have DRM on them.
Not disagreeing -
But, what would actually happen when someone who has no backups to their long collected personal collection of specific versions of songs
without thinking (yes, it happens) goes through the sync up with the cloud of the new apple music and assumes all is well and pushes the 'yes' button. Opps!
Hey, what happened to my personal stuff? Is this a bug or just the expected result of a clueless apple user? If a person's stuff is deleted, then it is an issue. Probably
more than extremely rare. People are a lot more clueless than you would think. So, some clearly stated results of pushing the 'yes' button is a good idea.