vtnet broken on -CURRENT when using VirtualBox

Hi list,
I'm observing a 100%-reproducible panic in the following setup:

Host system: FreeBSD 9.1-RELEASE-p7 amd64
$ pkg info | grep virtualbox
virtualbox-ose-4.2.18_1        A general-purpose full virtualizer for
x86 hardware
virtualbox-ose-kmod-4.2.18     VirtualBox kernel module for FreeBSD

System in a virtual machine: FreeBSD-CURRENT SVN rev 259064.
Virtual machine is created with virtio host-only adapter.

When trying to ssh into VM, the system in VM panics with the following
message:

panic: vtnet_txq_offload: mbuf 0xc309e900 TSO without checksum offload
KDB: stack backtrace:
db_trace_self_wrapper(c0b4fd4d,a6461,65393030,63333039,c13a29c0,...) at
db_trace_self_wrapper+0x2d/frame 0xc23f85a0
kdb_backtrace(c0b4b145,c0c29a7c,c0b9b43d,c23f865c,c23f865c,...) at
kdb_backtrace+0x30/frame 0xc23f8608
vpanic(c0c29918,100,c0b9b43d,c23f865c,c23f865c,...) at vpanic+0x80/frame
0xc23f862c
kassert_panic(c0b9b43d,c0b9b466,c309e900,8b1,c0dad504,...) at
kassert_panic+0xe9/frame 0xc23f8650
vtnet_txq_mq_start_locked(c2e02810,0,c0b9b369,8ea,c2e02810,...) at
vtnet_txq_mq_start_locked+0x62b/frame 0xc23f8808
vtnet_txq_mq_start(c2cf7800,c309e900,6,c23f89e0,c23f8866,...) at
vtnet_txq_mq_start+0x76/frame 0xc23f8834
ether_output(c2cf7800,c309e900,c23f89e0,c23f89d0,c36639d8,...) at
ether_output+0x64b/frame 0xc23f8888
ip_output(c309e900,0,c23f89d0,0,0,...) at ip_output+0x173f/frame 0xc23f8938
tcp_output(c36665e0,c342f400,32c,1,c36639d8,...) at
tcp_output+0x1cbf/frame 0xc23f8a9c
tcp_usr_send(c3410d40,0,c342f400,0,0,...) at tcp_usr_send+0x346/frame
0xc23f8ad0
sosend_generic(c3410d40,0,c23f8c10,0,0,...) at
sosend_generic+0x3b3/frame 0xc23f8b40
soo_write(c3142f50,c23f8c10,c2cf0d00,0,c3108620,...) at
soo_write+0x5d/frame 0xc23f8b70
dofilewrite(c3142f50,c23f8c10,ffffffff,ffffffff,0,...) at
dofilewrite+0x86/frame 0xc23f8ba8
kern_writev(c3108620,3,c23f8c10,0,28c4d608,...) at
kern_writev+0x96/frame 0xc23f8bf0
sys_write(c3108620,c23f8cc8,c23f8c98,c076b3a4,c0c36e90,...) at
sys_write+0x5c/frame 0xc23f8c40
syscall(c23f8d08) at syscall+0x2de/frame 0xc23f8cfc
Xint0x80_syscall() at Xint0x80_syscall+0x21/frame 0xc23f8cfc
--- syscall (4, FreeBSD ELF32, sys_write), eip = 0x2840dd77, esp =
0xbfbfb328, ebp = 0xbfbfb348 ---
KDB: enter: panic
[ thread pid 1570 tid 100065 ]
Stopped at      kdb_enter+0x3d: movl    $0,kdb_why
db>


Please help me to debug this.

-- 
Regards,
Ilya Bakulin