I just did a fresh install (not upgrade) of Precise Server 64-bit on a six 1.5TB RAID5 setup and I'm getting the same errors again.

$ sudo pvck /dev/md0
  Found label on /dev/md0, sector 1, type=LVM2 001

  Found text metadata area: offset=4096, size=2617344

$ sudo vgck -v HTPC
    Using volume group(s) on command line
    Finding volume group "HTPC"

$ sudo update-grub
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
Generating grub.cfg ...
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
Found linux image: /boot/vmlinuz-3.2.0-24-generic
Found initrd image: /boot/initrd.img-3.2.0-24-generic
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
Found linux image: /boot/vmlinuz-3.2.0-23-generic
Found initrd image: /boot/initrd.img-3.2.0-23-generic
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
error: unknown LVM metadata header.
Found memtest86+ image: /boot/memtest86+.bin
done

$ sudo mdadm --detail /dev/md0
/dev/md0:
        Version : 1.2
  Creation Time : Mon Apr 30 21:41:04 2012
     Raid Level : raid5
     Array Size : 7325678080 (6986.31 GiB 7501.49 GB)
  Used Dev Size : 1465135616 (1397.26 GiB 1500.30 GB)
   Raid Devices : 6
  Total Devices : 6
    Persistence : Superblock is persistent

    Update Time : Mon Apr 30 22:59:13 2012
          State : active, resyncing 
 Active Devices : 6
Working Devices : 6
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 512K

  Resync Status : 0% complete

           Name : htpc:0  (local to host htpc)
           UUID : 25f65ca0:f80f7b06:4f94157c:0b27a779
         Events : 5

    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/sda1
       1       8       17        1      active sync   /dev/sdb1
       2       8       33        2      active sync   /dev/sdc1
       3       8       49        3      active sync   /dev/sdd1
       4       8       65        4      active sync   /dev/sde1
       5       8       81        5      active sync   /dev/sdf1




No mention of any checksum errors or anything along those lines.

The six disks were setup with a RAID partition on each, creating one 7.5TB RAID volume over which LVM was added.

The only thing about this setup is that five out of the six disks are recycled from a previous mdadm setup with LVM. I did not run pvremove on any of the drives prior to the install.