The spare copy has been downloaded onto a spare folder onto user’s drives. It registers on the WU history as failed ‘Upgrade to Windows 10’ in the WU update history and a huge 3.5GB to 6GB hidden folder labelled ‘$Windows.~BT’.
This causes a few people who have low data caps and slow I\internet connections a bit of bother.
Microsoft has confirmed that individuals who have chosen to receive automatic updates through Windows Update, have been downloading the files they will need if they decide to upgrade.
It might explain why Microsoft has had such a high rate of downloads for Windows 10. After all people are technically downloading the software whether they use it or not.
If you have already downloaded the update you can get rid of it by opening the command prompt as admin and running: WUSA /UNINSTALL /KB:3035583. You also have to block updates and install them manually until Microsoft sees common sense.