panic: Duplicate free of item 0xffffff005c4a8600 from zone 0xffffff007fed4780(Mbuf)

Started running with debug.mpsafe=1.
Not shure if it has anything to do with it....

While running configure over NFS:

Slab at 0xffffff005c4a8fb8, freei 6 = 0.
panic: Duplicate free of item 0xffffff005c4a8600 from zone 0xffffff007fed4780(Mb
uf)

cpuid = 1;
KDB: stack backtrace:
kdb_backtrace() at kdb_backtrace+0x34
panic() at panic+0x1d2
uma_dbg_free() at uma_dbg_free+0x112
uma_zfree_arg() at uma_zfree_arg+0x10a
mb_free_ext() at mb_free_ext+0x96
m_freem() at m_freem+0x28
tcp_reass() at tcp_reass+0x1bb
tcp_input() at tcp_input+0x2af9
ip_input() at ip_input+0x94c
netisr_processqueue() at netisr_processqueue+0x8c
swi_net() at swi_net+0xe8
ithread_loop() at ithread_loop+0x18d
fork_exit() at fork_exit+0xc9
fork_trampoline() at fork_trampoline+0xe
--- trap 0, rip = 0, rsp = 0xffffffffb0bb5d00, rbp = 0 ---
KDB: enter: panic
[thread 100017]
Stopped at      kdb_enter+0x2e: nop

Coredump available.... 61Mb compressed.

system contains a de card, which is correctly identified as GIANT-LOCKED. The
card is not connected. Next time I open up the box, I'll remove it.

system info available at:
    http://withagen.dyndns.org/FreeBSD/cores/*.opteron

--WjW