lockmgr: thread 0xc385ebd0 unlocking unheld lock

Last night I was mounting a windows share with mount_smbfs and
browsing it via apache and I got the machine to panic twice. I was
tired and went to bed.
Today I can't replicate the panic but this always happens when I unmount:

lockmgr(c36cfb08,2006,c36cfb2c,c35251b0,d5926c00) at lockmgr+0x5c6
smb_co_put(c36cfb00,d5926c00,d5926c00,c35251b0,c3703280) at smb_co_put+0x46
smbfs_unmount(c33f6800,8000000,c35251b0,0,415) at smbfs_unmount+0x71
dounmount(c33f6800,8000000,c35251b0,c0733b28,0) at dounmount+0x286
unmount(c35251b0,d5926d04,c3527234,c,c35251b0) at unmount+0x1f6
syscall(3b,3b,3b,804a465,8201a51) at syscall+0x27e
Xint0x80_syscall() at Xint0x80_syscall+0x1f
--- syscall (22, FreeBSD ELF32, unmount), eip = 0x280c205f, esp = 0xbfbfe54c, eb
p = 0xbfbfe5f8 ---

Another time, a different share:

lockmgr: thread 0xc385ebd0 unlocking unheld lock
KDB: stack backtrace:
kdb_backtrace(c06ca09c,c385ebd0) at kdb_backtrace+0x29
lockmgr(c36ed508,2006,c36ed52c,c385ebd0,dab78c00) at lockmgr+0x5c6
smb_co_put(c36ed500,dab78c00,dab78c00,c385ebd0,c3703280) at smb_co_put+0x46
smbfs_unmount(c33f5400,8000000,c385ebd0,0,415) at smbfs_unmount+0x71
dounmount(c33f5400,8000000,c385ebd0,c0733b28,0) at dounmount+0x286
unmount(c385ebd0,dab78d04,c385d000,c,c385ebd0) at unmount+0x1f6
syscall(3b,3b,3b,804a465,8201a51) at syscall+0x27e
Xint0x80_syscall() at Xint0x80_syscall+0x1f
--- syscall (22, FreeBSD ELF32, unmount), eip = 0x280c205f, esp = 0xbfbfe53c, eb
p = 0xbfbfe5e8 ---

The machine is running CURRENT cvsuped last night with a kernel
compiled without a bunch of drivers. I can compile GENERIC if needed.

I'm trying to replicate the panic, and if I can I'll post a followup.
In the meantime if anyone can provide some insight on this or needs
more info I'm more than available.

--
Joao Barros