unable to "shrink" (via --grow) mdadm RAID

I have a 6xHDD RAID6, 2TB. (~2years old) Today I bought 2 new drives, wanted to expand my array.

fermulator@fermmy-server:~$ sudo mdadm --add /dev/md2000 /dev/sdq1
mdadm: /dev/sdq1 not large enough to join array

OH ... lovely ... the new drives are a tiny bit so much smaller.

Existing drives are:
fermulator@fermmy-server:~$ sudo fdisk -l /dev/sdk

Disk /dev/sdk: 2000.4 GB, 2000398934016 bytes
141 heads, 2 sectors/track, 13854713 cylinders
Units = cylinders of 282 * 512 = 144384 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xb277c3e5

   Device Boot      Start         End      Blocks   Id  System
/dev/sdk1               8    13854714  1953513560   fd  Linux raid autodetect

New drives are:
fermulator@fermmy-server:~$ sudo fdisk -l /dev/sdq

Disk /dev/sdq: 2000.4 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x1d99a245

   Device Boot      Start         End      Blocks   Id  System
/dev/sdq1               1      243201  1953512001   fd  Linux raid autodetect


fermulator@fermmy-server:~$ sudo mdadm -D /dev/md2000
/dev/md2000:
        Version : 01.01
  Creation Time : Fri Apr 22 01:12:07 2011
     Raid Level : raid6
     Array Size : 7814053632 (7452.06 GiB 8001.59 GB)
  Used Dev Size : 3907026816 (3726.03 GiB 4000.80 GB)
   Raid Devices : 6
  Total Devices : 6
Preferred Minor : 2000
    Persistence : Superblock is persistent

    Update Time : Wed Sep 25 00:40:21 2013
          State : clean
 Active Devices : 6
Working Devices : 6
 Failed Devices : 0
  Spare Devices : 0

     Chunk Size : 64K

           Name : fermmy-server:2000  (local to host fermmy-server)
           UUID : 15d2158f:5cf74d95:fd7f5607:0e447573
         Events : 12794

    Number   Major   Minor   RaidDevice State
       0       8      161        0      active sync   /dev/sdk1
       1       8      177        1      active sync   /dev/sdl1
       2       8      193        2      active sync   /dev/sdm1
       3       8      209        3      active sync   /dev/sdn1
       5       8      145        4      active sync   /dev/sdj1
       4       8      129        5      active sync   /dev/sdi1

BEFORE
	AFTER
Filesystem            Size  Used Avail Use% Mounted on
/dev/md2000           7.2T  6.1T  738G  90% /media/arrays/md2000

Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/md2000          7691438116 6527401064 773334372  90% /media/arrays/md2000
	Filesystem            Size  Used Avail Use% Mounted on
/dev/md2000           7.2T  6.1T  737G  90% /media/arrays/md2000

Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/md2000          7689826444 6527401064 771804620  90% /media/arrays/md2000

(shrunk ext4 filesystem by 1611672 1K-blocks = ~1,650,352,128bytes = 1.6Gb! -- should be plenty right?)

Now what?....

Now I have to shrink the array ...
http://webapp5.rrz.uni-hamburg.de/SuSe-Dokumentation/manual/sles-manuals_en/manual/raidresize.html#resizedecrraid

but it has no effect

fermulator@fermmy-server:~$ sudo mdadm -D /dev/md2000 | grep -e "Array Size" -e "Device Size"
     Array Size : 7814053632 (7452.06 GiB 8001.59 GB)

So ... if that value is in kbytes, I need to remove ~1611672 from it:
7814053632-1611672=7812441960
    --> 7450.52GiB

no luck though...

fermulator@fermmy-server:~$ sudo mdadm --grow /dev/md2000 -z 7812441960
fermulator@fermmy-server:~$ sudo mdadm -D /dev/md2000 | grep -e "Array Size" -e "Device Size"
     Array Size : 7814053632 (7452.06 GiB 8001.59 GB)

md2000 : active raid6 sdk1[0] sdm1[2] sdn1[3] sdj1[5] sdi1[4] sdl1[1]
      7814053632 blocks super 1.1 level 6, 64k chunk, algorithm 2 [6/6] [UUUUUU]

----
fermulator@fermmy-server:~$ cat /etc/issue
Ubuntu 10.04.4 LTS \n \l

fermulator@fermmy-server:~$ uname -a
Linux fermmy-server 2.6.32-49-generic-pae #111-Ubuntu SMP Thu Jun 20 21:44:04 UTC 2013 i686 GNU/Linux
fermulator@fermmy-server:~$ mdadm --version
mdadm - v2.6.7.1 - 15th October 2008