I first saw it over in a post by Andy Beal at Marketing Pilgrim, but in the post he lays the tracks to a whole epidemic of unauthorized name changes by top social networking service Bebo. It appears, at least from the mountain of bewildered queries on random web forums as well as Twitter that at least hundreds of folks are having their usernames changed, and are being refused any explanation whatsoever.
Andy and others who've documented this have said they've received emails that encourage folks to go check out the Bebo documentation for more information, but our scan of the help section offers very little helpful information on the matter.
It's not a particularly harmful change, and in many cases, all that's being added is an underscore to the name (at least in most of the cases I've seen documented). It is odd that it's going on, and the oddity is further compounded that no readily available information on the matter is available and that Bebo is offering no explanation when asked.