Updates appearing in Backup versions

I have linked several project plans to a resource pool and then created a master plan.

I then took a backup of all of the files into a folder called "backup" and worked on the original master file.

I have noticed that my updates on the master file are appearing in the backup like a mirror image. Is there any way that i can create a backup that is completely seperate to my update copy just incase i want to revert back to my backup.

Thanks,
G