reshape changing chunk size won't restart

[Andrew Burgess <aab@cichlid.com>]

mdadm 3.14
kernel 2.6.35.8

I started a reshape changing chunk size and after it ran
for a while i realized the disk i used for the
backup file was slow so I killed the mdadm
running in the background and tried to restart
with the new location (i moved the file just in case)

mdadm /dev/md5 --grow --chunk=8 --backup-file=/my/raid/RAID_BACKUP_FILE

it complains:

mdadm: /dev/md5 is performing resync/recovery and cannot be reshaped

/proc/mdstat for md5 shows partial progress but the numbers don't change
(except finish grows):

md5 : active raid6 sdd1[2] sdf1[8] sdc1[1] sdb1[0] sdh1[4] sdl1[5]  
sdj1[3] sdg1[7] sdk1[6]
       13674583552 blocks super 0.91 level 6, 128k chunk, algorithm 2  
[9/9] [UUUUUUUUU]
       [>....................]  reshape =  0.1% (2715648/1953511936)  
finish=850711.5min speed=38K/sec

The mdadm 3.14 is freshly compiled. I started the reshape
with mdadm 3.13.

I didn't try rebooting as the filesystem is mounted and
the data seems ok. Didn't want to make things worse...

Thank you for any help