Comment 2 for bug 1391429

I made some experiments and could only reproduce the problem with btrfs file system.
And /proc/mounts says the root file system is the snapshot. This is rather strange.
Probably it's a btrfs bug and nothing to do with grub-probe.

To reproduce:
1. Create an LV, format it to btrfs.
2. Mount the LV, create subvolume '@' on the file system.
3. debootstrap a base system to the subvolume.
4. chroot to the subvolume, do whatever it takes to make it bootable (install kernel, lvm2, btrfs-tools).
5. Boot the new system.
6. Create an LVM-snapshot of the root LV.
7. 'grub-probe --target=device /' will tell you that your root device is the snapshot.