Why would anyone buy a drive containing an OS, start putting stuff on it and then expect Bootcamp to partition and not mess it up? If this happens then great, but arguing the point of making a backup is stupid if you ask me.
I say keep all of your important files on that drive and partition away. Let bootcamp do it or do it in disk utility. While it is working start writing your post about how you partitioned a drive with data (other than an OS) on it that wasn't backed up somewhere else and and the data is now done.