Can't use old backups W/ Mavericks

[MMM]

Before we installed Mavericks a backup of 10.8.5 was made.

Trying to boot into the backup via startup disk, but even though the backup (10.8.5) is chosen, it just keeps booting back into 10.9 :(

I have double checked this by viewing the OS version under the 'apple' menu.

How can we fix this?

[dnanian]

Power off the Mac and disconnect the backup. Hold down Option and power on. When you get to the boot menu, attach the backup. Select it in the menu and start up from it, and see if that works.

[MMM]

Neat trick. THANKS Dave :D