I just have to believe they are testing something.  This type of thing did not seem to happen in earlier builds.  I wish I knew what was being downloaded first but I don't see any large files on my system.  Maybe it is going into the wrong place for the install but still gets removed after the update is complete.
Some folks are saying after the first download when it showed 0%, they would restart the system and the download went to basically done immediately.
Trouble, so far, no Blue Screens on the X99 system.  I will say the new Logo does not look good on a 5960x1080 display... 
Edit:  I just booted the X99 system from powered off and the Icons are set to 150% magnification again.  This is one of the symptoms of the video...