NFS panic: ^C on cp

Hi,
I'm using CURRENT r201138 and attending the 26C3, where we have access
to a NetApp filer (nfs://81.163.130.102/vol/fast, may work also for
external IPs).
It works well. But the following command sequence results with high
probability, not always, in a panic:
# mount_nfs -o nfsv3,rsize=32768,wsize=32768,intr 81.163.130.102:/vol/fast /mnt
# cd /mnt/
# cp some_large_file /some/where/local/
(wait a while)
^C
(panic: Assertion lk->lk_exslpfail == 0 failed at
/usr/src/sys/kern/kern_lock.c:962)

I
Backtrace:
Tracing pid 2754 tid 100209 td 0xc7580240
kdb_enter(c09ec974,c09ec974,c09c2936,eb402af4,1,...) at kdb_enter+0x3a
panic(c09c2936,c09e9af9,c09e98f2,3c2,c6511030,...) at panic+0x136
__lockmgr_args(daf26180,100000,0,0,0,...) at __lockmgr_args+0xe50
bqrelse(daf26120,0,c09f7b16,d3e,eb402c54,...) at bqrelse+0x44a
bufdone_finish(daf26120,daf26120,daf26120,0,eb402cbc,...) at
bufdone_finish+0x3ff
bufdone(daf26120,eb402c80,c8119080,eb402cbc,c06c7795,...) at bufdone+0x6a
nfs_doio(c8de7440,daf26120,c8119080,0,3c00,...) at nfs_doio+0x67b
nfssvc_iod(c0c23f80,eb402d38,c09e7dea,343,c7df3000,...) at nfssvc_iod+0x27c
fork_exit(c0878520,c0c23f80,eb402d38) at fork_exit+0xb8
fork_trampoline() at fork_trampoline+0x8
--- trap 0, eip = 0, esp = 0xeb402d70, ebp = 0 ---

With PID  2754 being: [nfsiod 0]

I didn't start lockd, if this matters. My /etc/rc.conf contains:
nfs_client_enable="YES"

The textdump is available here:
http://sites.google.com/site/lwfreebsd/Home/files/nfs-crash.tar.gz?attredirects=0&d=1
My kernel config:
http://sites.google.com/site/lwfreebsd/Home/files/kernelconfig-T400.txt?attredirects=0&d=1

Is there anything more I can do to track this bug further down?

Regards

Lucius