ZFS panic: wrong length 131072 for sectorsize 2352

[James R. Van Artsdalen]

amd64, svn 208373, in VirtualBox with no disc in the virtual CD drive.
...
Trying to mount root from zfs:CLANK
vdev_geom_open_by_guid:362[1]: Searching by guid [1976847806106852025].
vdev_geom_read_guid:230[1]: Reading guid from acd0t01...
panic: wrong length 131072 for sectorsize 2352
cpuid = 1
KDB: enter: panic
[ thread pid 2 tid 100009 ]
Stopped at      kdb_enter+0x3d: movq    $0,0x6cc120(%rip)
db> bt
bt
Tracing pid 2 tid 100009 td 0xffffff00028b8b40
kdb_enter() at kdb_enter+0x3d
panic() at panic+0x17b
g_io_request() at g_io_request+0x2a0
vdev_geom_read_guid() at vdev_geom_read_guid+0x226
vdev_geom_attach_by_guid_event() at vdev_geom_attach_by_guid_event+0x155
g_run_events() at g_run_events+0x217
g_event_procbody() at g_event_procbody+0x6c
fork_exit() at fork_exit+0x12a
fork_trampoline() at fork_trampoline+0xe
--- trap 0, rip = 0, rsp = 0xffffff800005cd30, rbp = 0 ---
db>
Tracing pid 2 tid 100009 td 0xffffff00028b8b40
kdb_enter() at kdb_enter+0x3d
panic() at panic+0x17b
g_io_request() at g_io_request+0x2a0
vdev_geom_read_guid() at vdev_geom_read_guid+0x226
vdev_geom_attach_by_guid_event() at vdev_geom_attach_by_guid_event+0x155
g_run_events() at g_run_events+0x217
g_event_procbody() at g_event_procbody+0x6c
fork_exit() at fork_exit+0x12a
fork_trampoline() at fork_trampoline+0xe
--- trap 0, rip = 0, rsp = 0xffffff800005cd30, rbp = 0 ---
db>