This has been going on for quite a while but I haven't had any solid proof until now.
Please search Google.com for "Princess Ivory Lace Tulle V Back Wedding Flower Girl Dress with Big Bow" and open up the first result:
(Forgive me for listing the URL prominently here as it facilitates understanding of the URL change)
Which is now a 404 not found error, a few days after the page was crawled by Google, when it was perfectly fine or Google wouldn't index the page in the first place.
Now when I do a catalog search, the exact product is now at a totally different URL:
See the different integer at the end of the URL key.
This has also happened quite some times with product pins on Pinterest.com that the URL of a particular product somehow automatically changes this way and the
Visit button of the pin leads also to a 404 not found page.
Apparently we never changed these URLs by ourself. Magento automatically changed them.
While I understand Magento has to append an integer of some sort to discriminate products with similar titles but why change it after it's been created?
Why? What could be the culprit here? How can we prevent it from doing this?