Comment # 5 on bug 937047 from Achim Gratz

(In reply to Thorsten Kukuk from comment #4)
> When you called snapper rollback, snapper told you that this snapshot is the
> new default root filesystem. What else do you expect?

It should be marked as such in the snapshot list or not be shown at all.  This
is simply a snapshot that snapper cannot deal with at that moment.

> snapper cleanup algorighm will not delete the subvolume with the current
> root filesystem. So this is can really only happen if you try to manual
> delete that snapshot.

Again, it shouldn't even try.  In my case I've included it in a range of
snapshots to delete, more or less by accident.