USB mass storage device oddness

I recently bought a USB Compactflash/SD/MMC etc etc reader which is causing
some strange problems. The device takes power from the USB socket and is made
by a company called PQI.
When I plug the device in with a CF card in the slot, /dev/da0s1 appears and
mounts fine. However, if I insert a card when the device is already plugged
in, the device becomes unuseable and occasionally, strange things will happen
to my system (that's the best I can describe it. I can't su or use sudo, I
can't open files with less, I can't Ctrl-C anything or kill anything, I can't
start and programs... In fact, I can't seem to open any files at all. But 
things already running continue to run fine.)

Any help or debugging advice gratefully received.

Details follow (LONG!):
FreeBSD uriel.mcgoldrick.org 5.1-CURRENT FreeBSD 5.1-CURRENT #8: Sat Jul  5
18:53:41 BST 2003     root_at_uriel.mcgoldrick.org:/usr/obj/usr/src/sys/URIEL
i386

Device attach messages:
Jul 11 19:11:11 uriel kernel: umass0: PQI Travel Flash, rev 1.10/2.05, addr 5
Jul 11 19:11:11 uriel kernel: umass0: SCSI over Bulk-Only; quirks = 0x0000
Jul 11 19:11:11 uriel kernel: umass0:0:0:-1: Attached to scbus0
Jul 11 19:11:11 uriel kernel: da0 at umass-sim0 bus 0 target 0 lun 0
Jul 11 19:11:11 uriel kernel: da0: <General Flash Disk Drive 2.05> Removable
Direct Access SCSI-2 device 
Jul 11 19:11:11 uriel kernel: da0: 1.000MB/s transfers
Jul 11 19:11:11 uriel kernel: da0: Attempt to query device size failed: NOT
READY, Medium not present
Jul 11 19:11:11 uriel kernel: (da0:umass-sim0:0:0:0): READ CAPACITY. CDB: 25 0
0 0 0 0 0 0 0 0 
Jul 11 19:11:11 uriel kernel: (da0:umass-sim0:0:0:0): CAM Status: SCSI Status
Error
Jul 11 19:11:11 uriel kernel: (da0:umass-sim0:0:0:0): SCSI Status: Check
Condition
Jul 11 19:11:11 uriel kernel: (da0:umass-sim0:0:0:0): NOT READY asc:3a,0
Jul 11 19:11:11 uriel kernel: (da0:umass-sim0:0:0:0): Medium not present
Jul 11 19:11:11 uriel kernel: (da0:umass-sim0:0:0:0): Unretryable error
Jul 11 19:11:11 uriel kernel: Opened disk da0 -> 6
Jul 11 19:11:11 uriel kernel: (da0:umass-sim0:0:0:0): READ CAPACITY. CDB: 25 0
0 0 0 0 0 0 0 0 
Jul 11 19:11:11 uriel kernel: (da0:umass-sim0:0:0:0): CAM Status: SCSI Status
Error
Jul 11 19:11:11 uriel kernel: (da0:umass-sim0:0:0:0): SCSI Status: Check
Condition
Jul 11 19:11:11 uriel kernel: (da0:umass-sim0:0:0:0): NOT READY asc:3a,0
Jul 11 19:11:11 uriel kernel: (da0:umass-sim0:0:0:0): Medium not present
Jul 11 19:11:11 uriel kernel: (da0:umass-sim0:0:0:0): Unretryable error
Jul 11 19:11:11 uriel kernel: Opened disk da0 -> 6
Jul 11 19:11:11 uriel kernel: da1 at umass-sim0 bus 0 target 0 lun 1
Jul 11 19:11:11 uriel kernel: da1: <General Flash Disk Drive 2.05> Removable
Direct Access SCSI-2 device 
Jul 11 19:11:11 uriel kernel: da1: 1.000MB/s transfers
Jul 11 19:11:11 uriel kernel: da1: Attempt to query device size failed: NOT
READY, Medium not present
Jul 11 19:11:11 uriel kernel: (da1:umass-sim0:0:0:1): READ CAPACITY. CDB: 25
20 0 0 0 0 0 0 0 0 
Jul 11 19:11:11 uriel kernel: (da1:umass-sim0:0:0:1): CAM Status: SCSI Status
Error
Jul 11 19:11:11 uriel kernel: (da1:umass-sim0:0:0:1): SCSI Status: Check
Condition
Jul 11 19:11:11 uriel kernel: (da1:umass-sim0:0:0:1): NOT READY asc:3a,0
Jul 11 19:11:11 uriel kernel: (da1:umass-sim0:0:0:1): Medium not present
Jul 11 19:11:11 uriel kernel: (da1:umass-sim0:0:0:1): Unretryable error
Jul 11 19:11:11 uriel kernel: Opened disk da1 -> 6
Jul 11 19:11:11 uriel kernel: (da1:umass-sim0:0:0:1): READ CAPACITY. CDB: 25
20 0 0 0 0 0 0 0 0 
Jul 11 19:11:11 uriel kernel: (da1:umass-sim0:0:0:1): CAM Status: SCSI Status
Error
Jul 11 19:11:11 uriel kernel: (da1:umass-sim0:0:0:1): SCSI Status: Check
Condition
Jul 11 19:11:11 uriel kernel: (da1:umass-sim0:0:0:1): NOT READY asc:3a,0
Jul 11 19:11:11 uriel kernel: (da1:umass-sim0:0:0:1): Medium not present
Jul 11 19:11:11 uriel kernel: (da1:umass-sim0:0:0:1): Unretryable error
Jul 11 19:11:11 uriel kernel: Opened disk da1 -> 6
Jul 11 19:11:11 uriel kernel: da2 at umass-sim0 bus 0 target 0 lun 2
Jul 11 19:11:11 uriel kernel: da2: <General Flash Disk Drive 2.05> Removable
Direct Access SCSI-2 device 
Jul 11 19:11:11 uriel kernel: da2: 1.000MB/s transfers
Jul 11 19:11:11 uriel kernel: da2: Attempt to query device size failed: NOT
READY, Medium not present
Jul 11 19:11:11 uriel kernel: (da2:umass-sim0:0:0:2): READ CAPACITY. CDB: 25
40 0 0 0 0 0 0 0 0 
Jul 11 19:11:11 uriel kernel: (da2:umass-sim0:0:0:2): CAM Status: SCSI Status
Error
Jul 11 19:11:11 uriel kernel: (da2:umass-sim0:0:0:2): SCSI Status: Check
Condition
Jul 11 19:11:11 uriel kernel: (da2:umass-sim0:0:0:2): NOT READY asc:3a,0
Jul 11 19:11:11 uriel kernel: (da2:umass-sim0:0:0:2): Medium not present
Jul 11 19:11:11 uriel kernel: (da2:umass-sim0:0:0:2): Unretryable error
Jul 11 19:11:11 uriel kernel: Opened disk da2 -> 6
Jul 11 19:11:11 uriel kernel: (da2:umass-sim0:0:0:2): READ CAPACITY. CDB: 25
40 0 0 0 0 0 0 0 0 
Jul 11 19:11:11 uriel kernel: (da2:umass-sim0:0:0:2): CAM Status: SCSI Status
Error
Jul 11 19:11:11 uriel kernel: (da2:umass-sim0:0:0:2): SCSI Status: Check
Condition
Jul 11 19:11:11 uriel kernel: (da2:umass-sim0:0:0:2): NOT READY asc:3a,0
Jul 11 19:11:11 uriel kernel: (da2:umass-sim0:0:0:2): Medium not present
Jul 11 19:11:11 uriel kernel: (da2:umass-sim0:0:0:2): Unretryable error
Jul 11 19:11:11 uriel kernel: Opened disk da2 -> 6

Messages when I insert a card:

Jul 11 19:12:01 uriel kernel: umass0: at uhub0 port 1 (addr 5) disconnected
Jul 11 19:12:01 uriel kernel: (da0:umass-sim0:0:0:0): lost device
Jul 11 19:12:01 uriel kernel: (da0:umass-sim0:0:0:0): removing device entry
Jul 11 19:12:01 uriel kernel: (da1:umass-sim0:0:0:1): lost device
Jul 11 19:12:01 uriel kernel: (da1:umass-sim0:0:0:1): removing device entry
Jul 11 19:12:01 uriel kernel: (da2:umass-sim0:0:0:2): lost device
Jul 11 19:12:01 uriel kernel: (da2:umass-sim0:0:0:2): removing device entry
Jul 11 19:12:01 uriel kernel: umass0: detached

/dev/da0s1 then fails to appear. (obviously)
When I get the following messages, the system begins playing up.

Jul 11 19:12:02 uriel kernel: umass0: PQI Travel Flash, rev 1.10/2.05, addr 5
Jul 11 19:12:02 uriel kernel: umass0: SCSI over Bulk-Only; quirks = 0x0000
Jul 11 19:12:02 uriel kernel: umass0:0:0:-1: Attached to scbus0
Jul 11 19:12:02 uriel kernel: da0 at umass-sim0 bus 0 target 0 lun 0
Jul 11 19:12:02 uriel kernel: da0: <General Flash Disk Drive 2.05> Removable
Direct Access SCSI-2 device 
Jul 11 19:12:02 uriel kernel: da0: 1.000MB/s transfers
Jul 11 19:12:02 uriel kernel: da0: Attempt to query device size failed: NOT
READY, Medium not present
Jul 11 19:12:02 uriel kernel: (da0:umass-sim0:0:0:0): READ CAPACITY. CDB: 25 0
0 0 0 0 0 0 0 0 
Jul 11 19:12:02 uriel kernel: (da0:umass-sim0:0:0:0): CAM Status: SCSI Status
Error
Jul 11 19:12:02 uriel kernel: (da0:umass-sim0:0:0:0): SCSI Status: Check
Condition
Jul 11 19:12:02 uriel kernel: (da0:umass-sim0:0:0:0): NOT READY asc:3a,0
Jul 11 19:12:02 uriel kernel: (da0:umass-sim0:0:0:0): Medium not present
Jul 11 19:12:02 uriel kernel: (da0:umass-sim0:0:0:0): Unretryable error
Jul 11 19:12:02 uriel kernel: Opened disk da0 -> 6
Jul 11 19:12:02 uriel kernel: (da0:umass-sim0:0:0:0): READ CAPACITY. CDB: 25 0
0 0 0 0 0 0 0 0 
Jul 11 19:12:02 uriel kernel: (da0:umass-sim0:0:0:0): CAM Status: SCSI Status
Error
Jul 11 19:12:02 uriel kernel: (da0:umass-sim0:0:0:0): SCSI Status: Check
Condition
Jul 11 19:12:02 uriel kernel: (da0:umass-sim0:0:0:0): NOT READY asc:3a,0
Jul 11 19:12:02 uriel kernel: (da0:umass-sim0:0:0:0): Medium not present
Jul 11 19:12:02 uriel kernel: (da0:umass-sim0:0:0:0): Unretryable error
Jul 11 19:12:02 uriel kernel: Opened disk da0 -> 6
Jul 11 19:12:02 uriel kernel: da1 at umass-sim0 bus 0 target 0 lun 1
Jul 11 19:12:02 uriel kernel: da1: <General Flash Disk Drive 2.05> Removable
Direct Access SCSI-2 device 
Jul 11 19:12:02 uriel kernel: da1: 1.000MB/s transfers
Jul 11 19:12:02 uriel kernel: da1: 30MB (62720 512 byte sectors: 64H 32S/T
30C)
Jul 11 19:12:02 uriel kernel: (da1:umass-sim0:0:0:1): READ(6)/WRITE(6) not
supported, increasing minimum_cmd_size to 10.
Jul 11 19:12:38 uriel kernel: (da1:umass-sim0:0:0:1): Synchronize cache
failed, status == 0x4, scsi status == 0x0
Jul 11 19:13:03 uriel kernel: (da2:umass-sim0:0:0:2): got CAM status 0x4
Jul 11 19:13:03 uriel kernel: (da2:umass-sim0:0:0:2): fatal error, failed to
attach to device
Jul 11 19:13:03 uriel kernel: (da2:umass-sim0:0:0:2): lost device
Jul 11 19:13:03 uriel kernel: (da2:umass-sim0:0:0:2): removing device entry
Jul 11 19:13:33 uriel kernel: Opened disk da1 -> 5

Apologies for the verbosity, but I really have no idea what is happening here.

-- 
Michael McGoldrick: mmcgoldrick_at_linuxdriven.net