Why can't I re-add my drive after partition shrink?

[Ram Ramesh <rramesh2400@gmail.com>]

I am trying to shring my mdadm underlying disks/partitions as a way of 
reclaiming space after md shrink operation. Here is my md
> Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] 
> [raid4] [raid10]
> md0 : active raid6 sdb1[6] sdg1[11] sdd1[12] sdf1[8] sde1[9] sdc1[10]
>       12348030976 blocks super 1.2 level 6, 64k chunk, algorithm 2 
> [6/6] [UUUUUU]
>       bitmap: 2/23 pages [8KB], 65536KB chunk
>
> unused devices: <none>

Here is my mdadm detail about /dev/sdb1
> Avail Dev Size : 11720780943 (5588.90 GiB 6001.04 GB)
>      Array Size : 12348030976 (11776.00 GiB 12644.38 GB)
>   Used Dev Size : 6174015488 (2944.00 GiB 3161.10 GB)
I fail, remove and repartition /dev/sdb1 so that new partition table 
looks like this. (No change to data obviously)
>    New partition table:
>    Number  Start (sector)    End (sector)  Size       Code  Name
>        1            2048      6442452991   3.0 TiB     FD00  Linux RAID
>        2      6442452992     11721045134   2.5 TiB     FD00  Linux RAID

Since new /dev/sdb1 is significantly bigger than what mdadm says that it 
is using, I thought I could simply re-add the drive. However, I get
> sudo mdadm /dev/md0 --re-add /dev/sdb1
> ***mdadm: --re-add for /dev/sdb1 to /dev/md0 is not possible***
Why? What did I miss here? Is it possible to fix this so that I can 
repartition other drives and -re-add them without having to go through 
full rebuild after each change?

I researched as much as I could on the net and came up with nothing 
except some one saying that mdadm keeps something at the end of the disk 
regardless of what it says about "Used Dev Size." Is it possible to move 
this info so that I could re-add?

Ramesh