After running a mirror backup a few times, I went into the backup properties for that backup and the backup type was selected on the left as full instead of mirror.
I wanted to switch it back to mirror but a warning came up stating if I change the backup type it would delete all my backup files.
As a test I ran the backup to see what it would do, and it's running a mirror backup instead of a full backup...

I then deleted the backup job from the list and then opened my backup *.fkc file again, went into properties and now it's mirror...

Is this a bug? If you want me to provide a video demo I can do.