zfs umnout lor

Hello,
I received the following LOR using current from:  Sun Mar 15 13:47:56
UTC 2009 on i386:

lock order reversal:
 1st 0x865d237c zfs (zfs) _at_ /usr/src/sys/kern/vfs_mount.c:1193
 2nd 0x86668058 syncer (syncer) _at_ /usr/src/sys/kern/vfs_subr.c:2205
KDB: stack backtrace:
db_trace_self_wrapper(806e8d4e,b2cc9a60,8054f456,80541bfb,806eb900,...)
at db_trace_self_wrapper+0x26
kdb_backtrace(80541bfb,806eb900,83c2cc38,83c2cca0,b2cc9abc,...) at
kdb_backtrace+0x29
_witness_debugger(806eb900,86668058,806f2854,83c2cca0,806f26d5,...) at
_witness_debugger+0x26
witness_checkorder(86668058,9,806f26d5,89d,0,...) at witness_checkorder+0x839
__lockmgr_args(86668058,80100,86668074,0,0,...) at __lockmgr_args+0x797
vop_stdlock(b2cc9bc4,8556d964,806f26d5,80100,86668074,...) at vop_stdlock+0x62
VOP_LOCK1_APV(80732080,b2cc9bc4,805039b2,8074c1c0,86668000,...) at
VOP_LOCK1_APV+0xb5
_vn_lock(86668000,80100,806f26d5,89d,808c297c,...) at _vn_lock+0x5e
vrele(86668000,0,806f208e,4ee,0,...) at vrele+0x142
dounmount(8402bc80,0,8556d8c0,47b,336,...) at dounmount+0x3ce
unmount(8556d8c0,b2cc9cfc,8,8556d8c0,80721a50,...) at unmount+0x2df
syscall(b2cc9d38) at syscall+0x2a3
Xint0x80_syscall() at Xint0x80_syscall+0x20
--- syscall (22, FreeBSD ELF32, unmount), eip = 0x28165f47, esp =
0x7fbfe39c, ebp = 0x7fbfe3c8 ---

I should mention that the fs that I was unmounting was created on a
usb device (maybe it's related to the new usb2 framework).
Thanks,
Dan