tape changer, but not tape drive

[Dan Langille]

I first encountered this problem in April, now I'm back to it:

   http://lists.freebsd.org/pipermail/freebsd-scsi/2008-April/003452.html

In short, the system has tape library.  The library has worked in the 
past (http://www.freebsddiary.org/digital-tl891.php) but now it does 
not.  I can see either the tape library or the tape drive.  Which I see 
depends upon the cable configuration.

   http://www.freebsddiary.org/images/tape-libraries-cables.jpg

As shown above, that's how I would expect things to work normally. 
However, in that configuration, I do not see the tape drive.  The cable 
going down, goes to the computer.  If I reconnect that cable to the plug 
to the left of the terminator, the system can see the DLT drive, but not 
the tape library.

Under 6.3-STABLE FreeBSD, I can see either one device or the other.

ch0 at ahc0 bus 0 target 0 lun 0
ch0:  Removable Changer SCSI-2 device
ch0: 20.000MB/s transfers (10.000MHz, offset 8, 16bit)
ch0: 10 slots, 1 drive, 1 picker, 0 portals

or

sa0 at ahc0 bus 0 target 1 lun 0
sa0:  Removable Sequential Access SCSI-2 device
sa0: 20.000MB/s transfers (10.000MHz, offset 8, 16bit)
acd0: FAILURE - INQUIRY ILLEGAL REQUEST asc=0x24 ascq=0x00 sks=0x40 0x00 
0x01

Any ideas?

Full dmesg output here:  http://www.langille.org/tmp/dmesg.boot

TIA.