Windows 7: Phantom drive in System Restore

To backup my boot drive I clone it to a drive plugged into a spare SATA port and then remove the backup drive and store it in the cupboard.

I now see that System Restore shows 2 C: drives: one, not available, with system restore turned on, and one, available, with system restore turned off.



If I turn system restore off on the phantom drive, it disappears from the list of drives. I then turn on system restore for the real drive C:, but of course it now has no restore points.

This is not an ideal situation, especially as I presume that if (when) my boot drive fails and I replace it with the backup drive that there will be no restore points available.

Any thoughts? BTW I have now assigned the backup drive a fixed drive-letter, just in case this helps.

Update I am doing the backup using Partition Wizard's Boot Disk and that way my restore points still exist.