"panic: sbappendstream 1" while using net/mpd

Hi,

I keep getting this panic on RELENG_6 when downloading data from a 
net/mpd link (GRE).

This GDB was configured as "i386-marcel-freebsd".
#0  doadump () at pcpu.h:165
165	pcpu.h: No such file or directory.
 	in pcpu.h
(kgdb) bt
#0  doadump () at pcpu.h:165
#1  0xc0631ea8 in boot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:397
#2  0xc06321bd in panic (fmt=0xc085d9c7 "sbappendstream 1")
     at /usr/src/sys/kern/kern_shutdown.c:553
#3  0xc066e296 in sbappendstream_locked (sb=0xc27f2050, m=0xc222b600)
     at /usr/src/sys/kern/uipc_socket2.c:741
#4  0xc06c8880 in tcp_input (m=0xc222b600, off0=20)
     at /usr/src/sys/netinet/tcp_input.c:1280
#5  0xc06c1c91 in ip_input (m=0xc222b600)
     at /usr/src/sys/netinet/ip_input.c:776
#6  0xc06a0cd6 in netisr_processqueue (ni=0xc096f7b8)
     at /usr/src/sys/net/netisr.c:235
#7  0xc06a0eba in swi_net (dummy=0x0) at /usr/src/sys/net/netisr.c:348
#8  0xc061f9b8 in ithread_loop (arg=0xc1e33480)
     at /usr/src/sys/kern/kern_intr.c:545
#9  0xc061edec in fork_exit (callout=0xc061f89c <ithread_loop>,
     arg=0xc1e33480, frame=0xd58d3d38) at /usr/src/sys/kern/kern_fork.c:789
#10 0xc07dc2dc in fork_trampoline () at /usr/src/sys/i386/i386/exception.s:208

I get a similar panic on RELENG_5 ("panic: sbappend") but I don't have 
a traceback right now.

-- 
jimmy