panic: sched_priority: invalid priority 3990 on r225375

I've gotten the following panic twice while running recent builds of
head under VirtualBox(FreeBSD 8.2 host).

panic: sched_priority: invalid priority 3990: nice 0, ticks 1227873280
ftick 175669871 ltick 175679894 tick pri 3818

The crashes happened while I was running a stress test of the network
stack.  I have a client machine and a server machine.  The client is
running head with a patch that I'm trying to prove out; the server
should be running with basically stock head as of r225375(I think that
there's a couple of minor changes in the tree I used to build the
server with, but I've gotten the crash on the client and the server,
and neither have any uncommitted patches in common).  The server is
running several netcat instances in listen mode; the client has a
script sitting in a loop starting netcat instances that connect to
instances running on the server and send data from client -> server.
The client also has a script that changes the routing tables
periodically.

Both the client and the server have crashed once so far.  I haven't
been running any tests on actual hardware so I can't say whether this
is a FreeBSD problem or a VirtualBox problem.  I'm going to start
running the same tests against VMs running some version of FreeBSD 8
to see if I can reproduce the problem there.  In the meantime, I've
made a core.txt accessible in case anybody wants to take a look.  You
can find it at:

http://people.freebsd.org/~rstone/sched_priority/core.txt.0.bz2

Please let me know if you need any more information.