I believe I have a similar issue, except dmraid does not activate the array. I've read a number of similar bugs, so I'll attach the outputs that I think might be useful:

ubuntu@ubuntu:~$ sudo dmraid -ay -vvvv -dddd
WARN: locking /var/lock/dmraid/.lock
NOTICE: skipping removable device /dev/sdc
NOTICE: /dev/sdb: asr     discovering
NOTICE: /dev/sdb: ddf1    discovering
NOTICE: /dev/sdb: hpt37x  discovering
NOTICE: /dev/sdb: hpt45x  discovering
NOTICE: /dev/sdb: isw     discovering
NOTICE: /dev/sdb: jmicron discovering
NOTICE: /dev/sdb: lsi     discovering
NOTICE: /dev/sdb: nvidia  discovering
NOTICE: /dev/sdb: pdc     discovering
NOTICE: /dev/sdb: sil     discovering
NOTICE: /dev/sdb: via     discovering
NOTICE: /dev/sda: asr     discovering
NOTICE: /dev/sda: ddf1    discovering
NOTICE: /dev/sda: hpt37x  discovering
NOTICE: /dev/sda: hpt45x  discovering
NOTICE: /dev/sda: isw     discovering
NOTICE: /dev/sda: isw metadata discovered
NOTICE: /dev/sda: jmicron discovering
NOTICE: /dev/sda: lsi     discovering
NOTICE: /dev/sda: nvidia  discovering
NOTICE: /dev/sda: pdc     discovering
NOTICE: /dev/sda: sil     discovering
NOTICE: /dev/sda: via     discovering
DEBUG: _find_set: searching isw_daeeifacja
DEBUG: _find_set: not found isw_daeeifacja
DEBUG: _find_set: searching isw_daeeifacja_RAID0
DEBUG: _find_set: searching isw_daeeifacja_RAID0
DEBUG: _find_set: not found isw_daeeifacja_RAID0
DEBUG: _find_set: not found isw_daeeifacja_RAID0
NOTICE: added /dev/sda to RAID set "isw_daeeifacja"
DEBUG: checking isw device "/dev/sda"
ERROR: isw device for volume "RAID0" broken on /dev/sda in RAID set "isw_daeeifacja_RAID0"
ERROR: isw: wrong # of devices in RAID set "isw_daeeifacja_RAID0" [1/2] on /dev/sda
DEBUG: set status of set "isw_daeeifacja_RAID0" to 2
RAID set "isw_daeeifacja_RAID0" was not activated
INFO: Activating GROUP raid set "isw_daeeifacja"
WARN: unlocking /var/lock/dmraid/.lock
DEBUG: freeing devices of RAID set "isw_daeeifacja_RAID0"
DEBUG: freeing device "isw_daeeifacja_RAID0", path "/dev/sda"
DEBUG: freeing devices of RAID set "isw_daeeifacja"
DEBUG: freeing device "isw_daeeifacja", path "/dev/sda"

ubuntu@ubuntu:~$ sudo dmraid -r
/dev/sda: isw, "isw_daeeifacja", GROUP, ok, 488397166 sectors, data@ 0

ubuntu@ubuntu:~$ sudo dmraid -s
ERROR: isw device for volume "RAID0" broken on /dev/sda in RAID set "isw_daeeifacja_RAID0"
ERROR: isw: wrong # of devices in RAID set "isw_daeeifacja_RAID0" [1/2] on /dev/sda
*** Group superset isw_daeeifacja
--> Subset
name   : isw_daeeifacja_RAID0
size   : 488391936
stride : 256
type   : stripe
status : broken
subsets: 0
devs   : 1
spares : 0

ubuntu@ubuntu:~$ sudo fdisk -l /dev/sda; sudo fdisk -l /dev/sdb

Disk /dev/sda: 250.0 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000

Disk /dev/sda doesn't contain a valid partition table

Disk /dev/sdb: 251.0 GB, 251000193024 bytes
255 heads, 63 sectors/track, 30515 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0xb8feb8fe

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1        3134    25165824    7  HPFS/NTFS
/dev/sdb2   *        3135       10914    62492850   83  Linux