raidframe puzzle

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

A particular -current/amd64 box has raid0-3 on a pair of SATA disks, and
raid4 on a pair of IDE disks. raid0-3 behaves as expected, but:

from dmesg:

wd0: GPT GUID: 0c870a1c-5dde-11e2-bea8-10bf48bd3389
dk0 at wd0: 0c870a22-5dde-11e2-bea8-10bf48bd3389
dk0: 625142381 blocks at 34, type: raidframe
...
wd1: GPT GUID: 14283eb1-5dde-11e2-bea8-10bf48bd3389
dk1 at wd1: 14283eb4-5dde-11e2-bea8-10bf48bd3389
dk1: 625142381 blocks at 34, type: raidframe
...
Component on: dk0: 625142381
   Row: 0 Column: 0 Num Rows: 1 Num Columns: 2
   Version: 2 Serial Number: 2013011400 Mod Counter: 1451820967
   Clean: Yes Status: 0
   sectPerSU: 128 SUsPerPU: 1 SUsPerRU: 1
   RAID Level: 1  blocksize: 512 numBlocks: 625142272
   Autoconfig: Yes
   Contains root partition: No
   Last configured as: raid4
Component on: dk1: 625142381
   Row: 0 Column: 1 Num Rows: 1 Num Columns: 2
   Version: 2 Serial Number: 2013011400 Mod Counter: 1451820967
   Clean: Yes Status: 0
   sectPerSU: 128 SUsPerPU: 1 SUsPerRU: 1
   RAID Level: 1  blocksize: 512 numBlocks: 625142272
   Autoconfig: Yes
   Contains root partition: No
   Last configured as: raid4
...
Found: dk0 at 0
Found: dk1 at 1
RAID autoconfigure
Configuring raid4:
Starting autoconfiguration of RAID set...
Looking for 0 in autoconfig
Found: dk0 at 0
Looking for 1 in autoconfig
Found: dk1 at 1
raid4: allocating 20 buffers of 65536 bytes.
raid4: RAID Level 1
raid4: Components: /dev/dk0 /dev/dk1
raid4: Total Sectors: 625142272 (305245 MB)

So all should be well... but

# raidctl -s raid4
raidctl: invalid device: raid4d: No such file or directory
# ls -l /dev/raid4*
brw-r-----  1 root  operator  18, 64 Jan  8  2013 /dev/raid4a
brw-r-----  1 root  operator  18, 65 Jan  8  2013 /dev/raid4b
brw-r-----  1 root  operator  18, 66 Jan  8  2013 /dev/raid4c
brw-r-----  1 root  operator  18, 67 Jan  8  2013 /dev/raid4d
...

?

raidctl -s raid0 is happy...

I can't spot the difference...

Cheers,

Patrick