I have always questioned Western Digital drive backup software that comes baked in to any new usb external drive. The first thing I do is repartition/format the thing but as some of the newer drives come with its own bios this isn't so easy to get around. Best thing you can do is simply choose an alternative backup drive--there are many to choose from!
http://smartphones.tgdaily.com/story/smartphones/os-x-mavericks-upgrade-destroys-data-rep/474538563761656e35456a66613765533934663377673d3d