This is a misconfiguration rather than a bug. Your array was degraded and so grub was only being installed to one of the disks, but your bios was continuing to boot from the other disk, with the old, now broken copy of grub.
This is a misconfiguration rather than a bug. Your array was degraded and so grub was only being installed to one of the disks, but your bios was continuing to boot from the other disk, with the old, now broken copy of grub.