SVN r221788: GEOM_PART: integrity check failed (da0, MBR); Western Digital "My Book"

[Brandon Gooch]

After r221788, I'm unable to mount my Western Digital "My Book"
NTFS-formatted USB hard drive.

This unit is straight-from-the-box; nothing has been
configured/reconfigured. It mounts successfully and functions
correctly in other OS environments I've tried (Windows 7 64-bit,
Ubuntu 10.10 64-bit, PC-BSD 9-CURRENT snapshot from early May, FreeBSD
9-CURRENT snapshot from early May, etc...).

The reason I'm pointing to the revision mentioned (from dmesg output):

...
ugen1.3: <Western Digital> at usbus1
umass0: <Western Digital My Book 1130, class 0/0, rev 2.10/10.12, addr 3> on usb
us1
umass0:6:0:-1: Attached to scbus6
(probe0:umass-sim0:0:0:0): SCSI status error
(probe0:umass-sim0:0:0:0): TEST UNIT READY. CDB: 0 0 0 0 0 0
(probe0:umass-sim0:0:0:0): CAM status: SCSI Status Error
(probe0:umass-sim0:0:0:0): SCSI status: Check Condition
(probe0:umass-sim0:0:0:0): SCSI sense: NOT READY asc:4,1 (Logical unit is in pro
cess of becoming ready)
(probe0:umass-sim0:0:0:0): Polling device for readiness
pass2 at umass-sim0 bus 0 scbus6 target 0 lun 0
pass2: <WD My Book 1130 1012> Fixed Direct Access SCSI-6 device
pass2: Serial Number 5743415A4134343831393132
pass2: 40.000MB/s transfers
GEOM: new disk da0
da0 at umass-sim0 bus 0 scbus6 target 0 lun 0
da0: <WD My Book 1130 1012> Fixed Direct Access SCSI-6 device
da0: Serial Number 5743415A4134343831393132
da0: 40.000MB/s transfers
da0: 1907697MB (3906963456 512 byte sectors: 255H 63S/T 243197C)
ses0 at umass-sim0 bus 0 scbus6 target 0 lun 1
ses0: <WD SES Device 1012> Fixed Enclosure Services SCSI-6 device
ses0: Serial Number 5743415A4134343831393132
ses0: 40.000MB/s transfers
ses0: SCSI-3 SES Device
pass3 at umass-sim0 bus 0 scbus6 target 0 lun 1
pass3: <WD SES Device 1012> Fixed Enclosure Services SCSI-6 device
pass3: Serial Number 5743415A4134343831393132
pass3: 40.000MB/s transfers
GEOM_PART: integrity check failed (da0, MBR)
...

The message regarding the integrity check seems to be emitted by code
from that revision.

What information can I provide to help troubleshoot the issue? I'm new
to GEOM troubleshooting...

-Brandon