This is a little joke from the WordPress developers.
I discovered this hidden “feature” two or three weeks ago, during my work on the website. I was trying to revert to a previous revision of an article and start comparing two identical revisions which has obviously no sense. I remember that at this instant, I was making an audio conference with a friend and he get a whole live transcription of the event, quite a bit scary at the very beginning ^^
If you know any other ones, let me know!