The fact that contact ringtones seems to be happening all over according to web forums, but no one seems to be providing any answers. I am so surprised that not even a single person is supplying a reason or a solution for this very serious bug.
Mine has been working since I set it up on the 4th. I have to remember on how I did it, but no issues so far. I took mp3s and assigned them to different people and work fine. How are you assigning them....I think you can do it from the "people" app or if you are playing the clip, assigning it from there.