WD Live backing up wrong amount of 'used' space

Initially I had about 100GB of space being used by my Mac. I deleted about 50GB, deleted the original backup, and tried doing a ‘fresh’ back up. WD Live keeps trying to back up the original amount. I tried rebooting WD Live, Mac etc. and it won’t back up the 50GB but instead the 100GB (not sure where it’s getting that extra 50GB anyway).

How are you making that backup? Are you just making a clean copy or do you use Time Machine or another app for the backup?