I just discovered the title of one of my books on Google Play (which had been for sale there for a year) had been changed, and a subtitle had been added. I was told this was because Google Play had been adding metadata from a third party partner.
My best guess is that this partner didn't have a listing for my book, but did have a listing for a book with a similar title by a totally different author, and somehow, staggeringly, my book title and subtitle were changed to that of the other book. I've changed the details back, and I'm hoping it doesn't happen again.
I may be the only one this has happened to, but anyone on Google Play might want to check their book details.