I just had the same error. I was trying to backup 186 gb to a 500gb drive and it says I don't have enough room left. Also this is how you send feedback to Microsoft: Providing Feedback to Microsoft
and this is how you would send feedback to Microsoft it this you were beta testing it: https://connect.microsoft.com/
Also if Microsoft still had Customer service longer then a month on non business OS's maybe they would catch these things before they made everybody think Microsoft is trash.
Which reminds me of a time I sent Microsoft a bug report and they asked me what technical service plan I was on and how I was going to pay for this service they were giving me. I told them that I was giving them a service and when they persisted I told them where to shove it.