I had the same thing happen to my c860. My fix was some packing peanut. I cut tiny bits of foam from the peanut, and placed it surrounding the button. it took me about 10 minutes to get it lined up and back together without foam falling out of place. I did that about a month ago, and I haven't had a problem since. I don't know how long the foam will last, but hopefully once it wears out it is just a matter of adding more to fix it.