I have the PB installed on a Macbook Air which I have now sold in order to upgrade to a Macbook Pro. In preparing the Air for a new owner I have disconnected all my accounts, and reformatted the drive, and launched a new OS X install. Problem is the install insists on installing El Capitan and not Yosemite. I tried returning to a pre El Capitan restore from time machine before reformatting but still the same issue. Can anyone tell me how to restore back to Yosemite?